Water Heater Problem

[Lost in LOS]

My friend has a problem with his electric on demand siemens water heater for his shower [heater in attic without apparent temperature adjustment. when he turns the shower to hot, no problem other than being very hot. when it turns it to cold, ok. he has a mixer valve on his shower and when he has to adjust it for a warm shower temperature it goes from warm then turns to cold so the only option is too hot or cold. I believe the water is so hot that you have to add too much cold and just a little of the very hot water. the on demand heater then thinks you don’t want any hot water since it is using very little of it and shuts down. any suggestions? there seems to be an adjustment on the water inlet to the heater in the attic from siemens but the plumber says it doesn’t do much

thanks for any help, I am from the states and we use a different system with a tank always kept hot

thanks

jimmy

[ZZZ]

As you say; the heater shuts down when the hot water flow is very low, this is to protect the heater. Most heaters have temperature selector so you can lower the temperature and in this way increase the flow.

If your friends heater don't have this temperature selector, hard to believe but possible, there is probably only three things you can do.

The not so easy solution would be to run the cold water via a cooler and thereby increase the need of hot water

You could fit another shower head with increased flow, this will increase the need for hot water.

What I would do is to get a new heater with temperature control

[chownah]

Sounds like you have a western style water heater. In the US water heaters are installed to provide a constant (more or less) temperature of hot water and all places where hot water is used are also supplied with a cold water line and usually a combination hot/cold valve system that mixes the hot and cold and is adjustable. If you think about it I think you will remember how many sinks and showers have a "joy stick" sort of handle which can be moved about to give different temperatures of water and different flow rates.....this control unit is supplied with both a hot and cold water line and the temperature is adjusted when the two are mixed in different proportions.

[technocracy]

Sounds like you have a western style water heater. In the US water heaters are installed to provide a constant (more or less) temperature of hot water and all places where hot water is used are also supplied with a cold water line and usually a combination hot/cold valve system that mixes the hot and cold and is adjustable. If you think about it I think you will remember how many sinks and showers have a "joy stick" sort of handle which can be moved about to give different temperatures of water and different flow rates.....this control unit is supplied with both a hot and cold water line and the temperature is adjusted when the two are mixed in different proportions.

Not a western style storage heater in this description. It's an on-demand kind of like a very large instanteous water heater ala an electric shower.

To me I think ZZZ hits the nail on the head that the heater is switching off due to the lack of water pressure (much as the small eletric showers do). There should be a temperature knob somewhere even inside under a cover he needs to turn it down - which sould resolve the problem as it will be set to supply water at a constant heat.

Large eletric water heater don't always advertise they have a temperature control - take my Stiebel Electron storage heater to adjust the temperature I have to remove the bottom plastic panel inside is an unmarked rotary knob which so happens to be the temperature control.

[technocracy]

That should of read Stiebel Eltron ....

[chownah]

I"m a bit embarassed...I didn't read the OP carefully enough and so my advice was not to the point....now I think I understand. I have a friend who had the exact same problem. The shower would run fine on hot but when you tried to modulate the temperature to a comfortable level you would get to the point where the heater would shut off and the shower would go cold. People have already mentioned the possibilty of adjusting the temperature setting to avoid excessively high temperatures at low flow rates...so...I'll mention another possibility. Some units detect the pressure differential between the inlet and outlet pressures and turn off when the difference is too low. This feature will shut off the heat when flow is too low....but also notice that it will also turn off the heat when the inlet pressure is too low. If the supply line to the heater is small diametre and if the cold supply line for the fixture branches off from the supply pipe for the heater then when the mixer is set to allow cold water to flow the pressure will drop on the inlet to the heater and the differential across the heater will drop and turn off the heater. If this is the problem then using a larger supply pipe for the heater can solve the problem or possibly rerouting the cold water line so that it taps into the water line at a larger supply pipe and not in the same small pipe supplying the heater.

[ProThaiExpat]

Fascinating suppositions so far, with chownah coming the closest to the correct diagnosis.

I have the offending water heater in both of my bathrooms and one of those bathrooms shares the heater with the kitchen, to which it is backed up.

It is a high end three phase electric water heater by Seimens, cost 9K baht with discount five years ago. it is supposedly automatic. The adjustment possible is to switch the internal wiring to reduce the amount of electricity used but when I tried this the water became too cold so the hottest temperature was not hot enough. Just before I gave up on the problem and went out and replaced the heater with one with a temperature knob, a fellow TV member told we what to do to solve the problem.

The supposition that water pressure and flow are part of the problem is correct. So how does one increase the flow of water through the heater without turning your water pump so high that it blows its own regulator, gasket head and other working parts, which I did, and I recently replaced my water pump as the pressure was set too high just to try to get past the water heater problem.

The solution is so simple, unless you want to tear out your bathroom wall and change your valves to water temperature control valves that may only be available in the West.

Turn on the sink spigot to full hot, then get in the shower and turn on the shower valve. The demand for water flow is high enough when you do this that the flow rate through the heater is high enough so it can't heat the water so hot that your valves can't handle it and the temperature in the shower is then adjustable for comfort without it turning to cold when it reaches that critical point when the hot is just about off and the cold is just about on.

Yes I know I am wasting water and electricity, but a least I can take a shower now with a comfortable water temperature level with my current equipment and plumbing. Fortunately I take short showers so this practice has not raised my water bill or electric bill noticeably.

If the OPs friend does not have a sink faucet on the same line with the water heater and the shower, I am suspect the best solution is to go out and buy a 5K baht adjustable temperature water heater and mount it to service his shower, perhaps the water pipe is easily accessible in the attic.

[ProThaiExpat]

Fascinating suppositions so far, with chownah coming the closest to the correct diagnosis.

I have the offending water heater in both of my bathrooms and one of those bathrooms shares the heater with the kitchen, to which it is backed up.

It is a high end three phase electric water heater by Seimens, cost 9K baht with discount five years ago. it is supposedly automatic. The adjustment possible is to switch the internal wiring to reduce the amount of electricity used but when I tried this the water became too cold so the hottest temperature was not hot enough. Just before I gave up on the problem and went out and replaced the heater with one with a temperature knob, a fellow TV member told we what to do to solve the problem.

The supposition that water pressure and flow are part of the problem is correct. So how does one increase the flow of water through the heater without turning your water pump so high that it blows its own regulator, gasket head and other working parts, which I did, and I recently replaced my water pump as the pressure was set too high just to try to get past the water heater problem.

The solution is so simple, unless you want to tear out your bathroom wall and change your valves to water temperature control valves that may only be available in the West.

Turn on the sink spigot to full hot, then get in the shower and turn on the shower valve. The demand for water flow is high enough when you do this that the flow rate through the heater is high enough so it can't heat the water so hot that your valves can't handle it and the temperature in the shower is then adjustable for comfort without it turning to cold when it reaches that critical point when the hot is just about off and the cold is just about on.

Yes I know I am wasting water and electricity, but a least I can take a shower now with a comfortable water temperature level with my current equipment and plumbing. Fortunately I take short showers so this practice has not raised my water bill or electric bill noticeably.

If the OPs friend does not have a sink faucet on the same line with the water heater and the shower, I am suspect the best solution is to go out and buy a 5K baht adjustable temperature water heater and mount it to service his shower, perhaps the water pipe is easily accessible in the attic.

To finish my post, others may think of innovative ways to increase the water demand in the shower if the sink faucet is not inline with the shower and those may be to install a spigot on the same line as the shower so water can be drawn at the same time as I do with my sink spigot or better yet, install multiple shower heads in the shower so you have multiple sprays on your body and thereby increasing the water demand in the shower and shortening the time the water is passing over the heater coils.

[chownah]

I thought of an experiment that might help to diagnose the problem. Turn the shower on with only hot water....not cold at all....and then trottle it down lower and lower with still hot water alone to see just how low the flow can be and still have the water running hot. If the hot water alone can be throttled way down to a really slow setting...slow enough that the addition of cold should dilute it enough for a warm instead of hot shower...then it would seem that it is not the temperature limiter that is turning the hot off during the shower....but it does not eliminate the possibility that a lack of pressure differential across the water heater is turning it off.

Please try this and let us know what happened.

Chownah

[ProThaiExpat]

Chonwah: Your test reveals the following result. When the hot water demand reaches the exact point where is is calling for little or almost no hot water and just before the cold water demand starts, the water heater turns off with an audible click. Pushing the hot back up slightly clicks it back on.

It may well be that the type of joy stick type shower valve doesn't mix the water properly. In any case, tearing out the tile and putting in a new valve isn't a viable option in my view. As I posted, I was going to replace my Seimens Automatic Water Heater with a Japanese one with a temperature knob on the front when a fellow TVer gave me the solution that I use now, running the sink at full hot so the demand for water through the heater is high enough so the water passing through the copper heating coil moves so rapidly as to not heat it so much.

I am intrigued by my last thought that we could be enjoying multiple shower jets or heads in our shower with this heater as it seems to thrive on hot water demand. I will explore the possibility of getting a Y valve to place between my exit pipe and my shower head and see if doubling the water outlet demand will work the same way as turning on the sink at the same time as showering.

By the way, when I replaced my busted pump due to too high a pressure setting over the years, my replacement has remained at the factory setting so the pressure to my bathroom has been reduced from before but the sink and shower on at the same time still works. When you think about it, the shower head reduces the amount of water exiting the shower pipe and thus causes a back up of pressure that causes the water to pass through the heating coil slower than if one were to remove the shower head. A good test would be to remove the shower head and see if the system works better. This would be proof positive that more hot water demand at the shower is the solution to the problem as presently plumbed.

[chownah]

ProThaiExpat,

Thanks for testing my idea. When you have the hot water only flowing at its lowest point just before the heater makes the click and turns off....at that point is the hot water coming so slowly that you would think that if you could maintain that flow of hot water when the cold water is also on that it would make a good shower of moderate temperature?....or would you judge that even at that flow there is too much hot water to get a moderate shower even when the cold is added?

Chownah

P.S. I'm not sure if I was clear before but in my scenerio the solution would be a larger diameter pipe to the water heater and possibly isolating the cold water line from the hot water line (two supply pipes from the feeder line...one for the heater and one for the cold)..which might not be a practical fix for everyone but it might be possible for jimmy's friend whose water heater is installed in the attic.

Chownah

Edited July 13, 2007 by chownah

[ProThaiExpat]

chonwah: The flow does not diminish as one moves the handle from very hot toward the cold. I did not try reducing the flow to the head by pushing the handle toward the wall. This maneuver lessens the flow to the head and causes the heater to click off even sooner.

I am familiar with temperature sensitive valves that one buys in the West for use in condo buildings that have a communal water system so you shower doesn't constantly run hot and cold and every temperature in between as other condo residents use their showers at the same time.

If I knew what I know now about this particular heater, I would not have bought it obviously. If I did, I would have tried for a temperature control mixer valve.

I have learned one thing from this exchange. That my water heater has a temperature thermostat that shuts if off when not enough water runs through it, thereby protecting the unit from overheating when there is insufficient water to heat.

In summary, I think it is a great water heater that delivers a great quantity of hot water, but that is the problem, too much of a good thing.

[ProThaiExpat]

PS: Any solution that causes more water to run through the heater at any one time, thereby reducing the time the water is exposed to the heating coil, is the way to remedy the problem. It seems to me that increasing the demand side is cheaper in the long run than increasing the supply side as even if you double the supply side flow, if the demand side is much less due to the shower head or other device to spray the water, then there will be a back up on the supply side that will negate the supply side doubling of flow.

As I said, I have no problem iwth the supply side as increasing the supply side flow by increasing the pressure by the pump didn't due the trick. The only thing that seems to work is increasing the demand side, the way I do it is with turning on the bathroom sink. Another way would be to put a spigot in the shower or another shower head. Perhaps a very high demand shower head may be enough although when I turn my high end shower head to maximum flow, still no joy.

[chownah]

I have learned one thing from this exchange. That my water heater has a temperature thermostat that shuts if off when not enough water runs through it, thereby protecting the unit from overheating when there is insufficient water to heat.

If this is the case then my scenerio does not apply to your heater. My scenerio would apply to heaters that turn the heat off at low flows by sensing the difference in pressure between the inlet and outlet sides of the heater.....flow is directly related to pressure difference and visa versa. In some water heaters, for instance, when you turn the hot water off the flow goes to zero and the pressure difference betweent the inlet and outlet goes to zero and this turns off the heat.....I guess yours works on a different principle.

Chownah

Edited July 13, 2007 by chownah

[ProThaiExpat]

Don't mean to quibble and perhaps I misled you by something not said correctly.

My heater turns off when there is insufficient demand for hot water so there is danger that the low level of water through the heating coil, the pressure therein, is too low and overheating would result.

When my shower valve reaches the point that the hot water demand side of the valve is at minimum and the cold water side is about to cut in, the heater shuts off due to no sufficient demand. Perhaps my Cotto shower valve does not in fact mix the water at all but merely provides hot water and cold water.

This would explain why the water goes from too hot to only cold with no in between temperature.

By turning on the sink at full hot, I create so much demand for hot water when I turn on my shower also, that the water heater only produces moderate hot water. This explanation does not hold up because when I have the sink on full hot, the shower valve works normally, that is, I can regulate the temperature as one would expect in a normally working shower valve. So some mixing must occur in the valve or I couldn't regulate temperature with the valve.

Perhaps, if the heater is producing water so hot that the amount of cold water required to make it usable is so great that the mixing valve operates to restrict the hot water to the point that the hot water demand side of the valve calls for too little hot water and the heater shuts off due to a lack of hot water demand. That is my only guess. In other words, only so much water is allowed by the valve to flow through and if too much cold is called for by the position of the valve (inorder to cool the too hot water) the hot water demand side is necessarily restricted to the point the heater shuts off.

[chownah]

My heater turns off when there is insufficient demand for hot water so there is danger that the low level of water through the heating coil, the pressure therein, is too low and overheating would result.

When the heater has very little water flowing through it...when it is almost turned off...the pressure is not low in the heater...that is when the pressure is at its highest. When the hot water is turned completely off is when the pressure is highest in the heater. When the heater is off the pressure is high at the inlet and high at the outlet...there is not difference between these pressures and so the heat is off. If you open the tap and let just a bit of water flow throught the heater then the pressure at the outlet will drop slightly and the pressure difference between the inlet and outlet will be small and perhaps the heat will not come on. If you continue to increase the flow rate the pressure will drop even more at the outlet (and just as an aside it will also drop slightly at the inlet but not nearly as much as at the outlet) you will reach a point where the pressure difference between the inlet and the outlet will reach a certain amount and the heat will come on...at least this is how some hot water heaters work. They sense the difference in pressure between the inlet and the outlet....if this is low it means that the flow is low and if it is high then the flow is high...high enough difference means high enough flow and the heat comes on...low enough difference means low enough flow and the heat goes off.

My scenerio is that when the cold water is turned on in some installations this causes the pressure to drop at the inlet to the heater and since the inlet pressure is so low there is not enough pressure difference between the inlet and outlet to keep the heat on. In this case the cure is to stop the cold water flow from lowering the pressure at the inlet of the water heater....one way is to use a larger supply pipe and another way is to get the cold water from some other feeder line so the cold water flow has less influence on the water flow to the heater....this should also increase the flow through the shower head as the result would be an oveall increased water pressure at both the cold and hot supplies....so in a certain way it is almost like some of your suggested fixes.

Sorry, but I've got to call it quits for today....I'll check back in tomorrow.

Chownah

Edited July 14, 2007 by Totster
edited at members request

[ProThaiExpat]

Chonwah: Quite right. I kept intermingling water pressure with volume in my comments. Adopting your thesis that the water heater detects the difference between the inlet and outlet pressure and turns on accordingly, that explains that the heater turns off by the same mechanism and does not operate with a thermostat as I postulated.

Your thesis seems correct since, if a thermostat was involved, it would limit the temperature of the water heated and that doesn't seem to be the case. The hot water at max seems to be scalding in temperature. We seem to get hung up on is the ability of the valve to mix the cold and the hot to get a comfortable temperature.

It seems, upon reflection, that it is the inability of the shower valve to mix the exceedingly hot water volume delivered by the heater, (and that volume is necessary to make the heater cycle on} with enough cold water so that the temperature exiting the shower head is comfortably warm. The rated capacity of the shower valve may be the problem. My valve cannot handle the volume of hot water, necessary to pass through the heater, to allow it to operate, and simultaneously handle the volume of cold water necessary to cool that exceedingly hot water volume delivered to the valve and mix the two successfully.

My only point of disagreement with you at this point is your supply side thesis. Without expanding the outlet side of the system, the volume of water cannot increase to a level high enough to activate the heater. However, if your point is that it matters not the volume of water passing through the heater but the difference in the pressure between the inlet and outlet side that controls, then I have no evidence to the contrary.

I must admit that I suspect your right since there have been times when my water pump was not working in the past and yet I got hot water with the extremely low pressure water delivered to my house from the municipal water works. Even when that condition existed, I still had the problem with too hot and then no hot at a certain point with the valve handle. Thus is must be the difference in the relative pressures between the inlet and outlet sides of the heater that controls its operation. In Germany where this heater, undoubtedly, is designed to operate, valve capacity may well be greater or of a type that controls temperature and the heater only operates as full on and full off.

As I mentioned in my first post, this heater does provide a wiring schematic that allows the installer to choose between 8 volts and 12 volts. Mine is wired for 12 volts, as the 8 volt configuration doesn't deliver hot enough water, even at full hot. When I was operating at the 8 volt configuration, the water was comfortable at full hot during the summer when the water delivered to the heater from my tank was much warmer than in the winter when it was much colder.

Thanks chonwah for patiently taking me through this scenario, so I understand the system so much better now.

[ZZZ]

Interesting problem that I'm sure many more have here in Thailand.

I don't thing the pressure difference has anything to do with this problem. The pressure within the system is equal at all times as pressure distributes equally within a vessel. The only pressure difference you will see is between the water pressure inside the shower head and outside the shower head, the pressure inside the shower head will be the same as at the intake to the water heater.

Most heaters I have seen have two control devices.

One regulates the power to the heater, in your case the 8V or 12V setting. In other systems you have a knob you can turn that will regulate how much power to be used by the heater element or in some cases this is a thermostat that will regulate the water temperature in the heater.

The other control is a flow meter. This is often a ball bearing ball inside a vertical pipe in your heater. When the water flow through this pipe it will lift the ball up to a magnetic switch that will start the heater element. As you decrease the flow from the water heater the ball will drop and the heater element will switch off.

As I said in my first post there are three things you can do:

The reason there are problems with these heaters in Thailand is that the temperature difference between the cold water and the required shower temperature is normally very small. The amount of hot water required to increase the cold water temperature to comfortable shower temperature is to small for the flow meter in the heater. These systems often work ok in the winter time or in the morning but in the afternoon when the cold water is hot you can have problems. So one solution would be to in some way make your cold water colder.

Another solution is what you are doing now, increase the flow by turning on another outlet. I use a large (1 foot) shower head, this allows a flow many times greater than from a normal shower head.

Third solution is to have a heater with more settings than your 8V, 12V heater. Most household heaters have knob where you can tune in the desired setting. In your case the selections you have is just outside the limit to give you a comfortable setting, a 10V setting would probably be perfect. This could probably be achieved by changing a resistor or two in your control system, but get a professional to do this.

[ProThaiExpat]

Spot on ZZZ!!!

[Rooo]

I had the same problem with my Siemens system. Make sure the wiring is correct. You have 3 settings.I ended up getting the manual from Siemens , in German sorry as my builder threw the original out.I have attached it.I ended up rewiring the correct setting & cleaned the outlet at the shower tap & head & increased the water pressure.

[nantawan]

Thanks for the manual of Siemens. I cannot read German but it's still good to have

[roietjimmy]

I have suffered the same in condos and houses before using on-demand water heater systems. Hopefully, the suggestions you are getting in the post will fix the problem but if not, I suggest a more radical but somewhat more expensive solution. Replace the on demand heater with an electric boiler. I know boilers use more electricity than on demand systems but I have used a Ferroli brand boilers in both condos and my new home and have never experienced any hot/cold water mixing problem. They offer sizes from 15 litre to 320 litre. I have forgotten the exact prices but they are reasonable. I'm sure Home Pro or some other hardware supplier has them in stock. Hopefully there is enough space in your attic to simply remove the on demand heater and replace it with the boiler.