Mitsubishi WP105Q not switching off

[surat04]

I installed this pump at my MIL house about 8 years ago. Last year I replaced the pressure tank as the original developed a leak and it has worked well until recently. It now runs continuously and will not cut out. I have replaced the pressure switch and installed a new foot valve and supply pipework. I also removed the black hexagonal assembly (not sure what its called) cleaned it and checked for damage. After all this the pump will still not cut out. Pressure tank has been drained also. When the pump is running the pressure at the tap seems lower than before this problem started. Anyone have any ideas how to solve this problem.

[lopburi3]

Are you using water due to a leak by any chance? You mention pressure seems lower? Can check storage tank and see if water is going down when not using anything in house. If pressure lower the pump is probably good and not getting up to the cut off pressure needed. There could be a pipe or connection burst or perhaps a toilet running that has not been noticed. If you have a shut off valve immediately after pump easy to check by closing as see if pump builds pressure and stops - but if no shut off before pipes go out of sight you can use the check of storage tank level to see if water is being lost.

[surat04]

There is a valve at the pump to shut off supply to the house but closing this does not stop the pump. It is pumping from a well and there is plenty of water.

[wayned]

I have had an old Mitsubishi 150 that was doing the same thing. The impeller in the pump was worn, most likely do to the high mineral content in the local water. The pump could never develop enough pressure to cause it to shut off. In the end I just bought a new pump.

[surat04]

If I have to buy a new pump does anyone know what the difference is between the QS and Q5 series.

WP105QS is 4,200 baht in BigC

WP105Q5 is 5200 baht in a local pump shop.

[wayned]

I think that the Q5 is just a newer model pump. 5200 baht seems high, Home Pro Direct to shop has the Q5 for 4190 baht, https://www.directtoshop.com/product/1049594

[Pib]

Based on what the OP has troubleshot/changed so far it could be low line voltage. I know when I experience low voltage in my area (not often thankfully), if the voltage drops to around 180V versus the normal 225V my Mitsubishi WP255Q pump will just run and run trying to rebuild full pressure...basically the pump motor can't turn fast enough due to the low voltage to reach cut off pressure for the pressure switch. Check the MIL line voltage...if it not with 10%=15% of normal 225V that could be your problem

Also, I wonder if the pump is receiving adequate water input....if the water input is low/has air in it the pump can't reach full pressure to cut off.

[surat04]

Based on what the OP has troubleshot/changed so far it could be low line voltage. I know when I experience low voltage in my area (not often thankfully), if the voltage drops to around 180V versus the normal 225V my Mitsubishi WP255Q pump will just run and run trying to rebuild full pressure...basically the pump motor can't turn fast enough due to the low voltage to reach cut off pressure for the pressure switch. Check the MIL line voltage...if it not with 10%=15% of normal 225V that could be your problem

Also, I wonder if the pump is receiving adequate water input....if the water input is low/has air in it the pump can't reach full pressure to cut off.

Thanks for the reply. The problem has been ongoing for about 2 weeks now. I have been away so only yesterday started to look at the problem. Would low voltage persist constantly for 2 weeks? They have never had that problem before. Unfortunately I don't have anything to test the supply voltage with.

Water input should be fine. I replaced everything on the supply side and the water level in the well is about 4 meters above the foot valve.

[Pib]

I've seen plenty of posts on ThaiVisa who must put-up with low voltage almost every day. You can get low cost voltmeters at lots of places...Lotus, Amorn Electronic, Homepro, etc. Just saying my pump just runs and runs trying to rebuild/reach cutoff pressure when the voltage drops below 180V or so. Something to check. Good luck.

[wayned]

I have low voltage all of the time. I put a cheap digital voltmeter in an unused socket and leave it there.. They are available fro Aliexpress for about #3.50 When I get low voltage or a power out I turn off the pump and connect to the local water system. I am currently using a 255Q3 for the house and either usually it won't start with low voltage and it kicks out the thermal overload switch. I can't imagine low voltage of two weeks. As I said I had a bad impeller in a past pump and it would run forever and never build up enough pressure to turn it off. Here's a picture of the meter.

[Pib]

Something else just come to mind since we've talked low voltage in the last few posts. The pump motor "start/run capacitor" may be going or is completely bad. The capacitor is located in the plastic box on top of the pump assembly....it will usually be rectangular in shape with 2 to 4 leads...about half the size of a pack of cigarettes. This capacitor feeds some of the motor windings causing a voltage lag/phase shift which provides the correct rotating magnetic field to cause motor rotation, speed/torque build-up, and maintaining speed/torque.

It works just like the start/run capacitor in a common floor/desk fan. When the capacitor is bad or going bad the fan will show symptoms such as slow start up or maybe not even starting, takes much longer than normal to reach full speed, and if you wanted to do a test by holding the fan blade of a fan with a good start/run capacitor compared to one with a defective start/run capacitor you would feel the stronger torque of the fan with the good capacitor..

Depending on the condition of the capacitor different people can experience different low voltage levels as to where their same model pumps just runs and runs trying to build up enough speed/pressure to reach cut off pressure. That is, one person's pump may be able to reach speed/pressure at say 180V but another person's identical pump may not. Now you just can't pair any size start/run capacitor with a motor as each motor has a certain capacitor size it is designed to work best with.

Anyway, pump, fan and A/C compressor or fan start/run capacitors are low cost and run capacitors are easily found in stores like Lotus, Amorn Electronic, electrical section of a hardware stores, etc. A/C start capacitors are easily found at stores like Amorn...and cost around Bt150. Pretty easy and fast to change also with some basic tools. Be sure to cut electrical power to the motor when changing the capacitor.

I expect the start/run capacitor on the OP's WP105 pump is in the 4 to 8 microfarad ballpark (my WP255 uses an 8 microfarad)...it will cost around Bt50. I have a spare on hand as they do and will fail...but failure is usually not often like compressor start capacitors on A/Cs which have a bad habit of failing in the 5 to 10 year point (or sooner). They are also easy to change....just be sure to disconnect power to the electrical pump when changing (just to repeat). For an A/C it usually has a separate start capacitor about the size of a small cola can and costs around Bt150 and a separate fan run capacitor which is very similar to the start/run capacitor on the water pump motors like we are talking about....same cost of around Bt50.

If a person had a low cost multimeter that also included capacitance measurement along with typical voltage & resistance measurement capability a person can check to see if the capacitor capacitance is plus or minus X-amount (usually 10%) of the rated capacitance. When capacitors fail they usually either "open up completely/acts like an open circuit/broke wire" or the capacitance become significantly lower. When a start/run capacitor opens up it may not even allow a motor to start up as it can build-up enough torque to overcome starting resistance or will start-up slowly but can't reach full speed/torque. For a water pump motor if it can't reach full speed it won't be able to reach full pressure/pumping capability but would continue trying until it overheated and shutdown.

The Mitsubishi WP pumps have a thermal relay built into the motor windings which trips just like a circuit breaker when the motor gets too hot like when it has run too long...some water pump motors are not made for continuous running. Once the thermal relay is tripped and the motor/relay cools off sufficiently which usually takes 15 to 45 minutes the relay will automatically reset and the motor will start running again until it overheats and the thermal relay trips again....the cycle can go on and on and on until the motor/thermal relay finally just burns up/fails completely and permanently.

P.S. Just last year I fixed two of the MIL's fans as their run capacitors had finally went bad. One was in a big ceiling fan, the fan would start up very slowly and not spend fast like it use to...this run capacitor was probably 25 years old. And I replaced the run capacitor in a floor fan (probably 10 years old) that would barely start...would take about 2 minutes to build up speed or sometimes you would need to kickstart the fan blade to get it turning initially. New start capacitors from Amorn at around Bt50 each fixed both of those fans.

[surat04]

The start capacitor was replaced just over 4 months ago, so I have assumed that it is OK. When the original capacitor failed the pump would not start.

[Pib]

OP,

Are you sure, double sure, you are getting enough water to the input of the pump? You said the well has plenty of water but how do you know that? In this drought many wells have been drying up/running low

A WP105 is a small capacity pump and probably running one tap full open, for sure with two taps full blast, the pump would run all the time, but you would know if you have taps on...and hopefully a leak causing the same problem unless the leak is out of sight/below ground/under the house/etc. Can you isolate the pump output from the output lines to check for leaks you can't see....like do you have a cutoff valve right at the pump output?

Also the pressure switch you replaced was it the correct pressure range which should be approx 1.2 bar cut-on, 1.8 bar for cut-off? If the wrong switch was installed, like a switch for my WP255 pump which uses 2.1/2.8 bar switch, your WP105 wouldn't be able to reach that 2.8bar pressure and run all the time.

I don't mean to sound like a prosecuting attorney, it just your kind of problem with the pump "always running" even with no water being used/no taps on is usually caused by inadequate water "input," bad/wrong pressure switch, or a major leak out of site.

That black, hexagon thing you referred to is the air balance control/air control value...it ensures the right amount of air is maintained in your pump's pressure tank/keep the tank from getting water logged over the long term. A water logged tank can cause a pump to run durn near continuously (over 80% of the time) when very little water is being used...even a small amount caused by a small leak.. But even with a defective air balance valve, such as a pin-hole size leak in the valve rubber diaphragm/very hard to see without very close examination (I've had that problem on my WP255) but "completely" draining the pump's pressure tank to let air enter the drain valve will provide the necessary air in the tank to work perfectly-fine for a few days to maybe a few weeks with a totally defective/no air balance control valve at all. But over the long term that air is slowly absorb into the water since no rubber bladder is used in this pressure tank particular design and the pressure tank slowing become water logged again without a functional air balance control valve.

Good luck in finding the problem. And once again, I don't mean to sound like a prosecuting attorney...just throwing some "what ifs" out there for your consideration. Cheers.

[surat04]

When I replaced the foot valve and input pipe I had to withdraw the old pipe from the well. It was wet 4 metres above the old foot valve. That's how I know there is enough water in the well. As previously said there is a shutoff valve on the pump outlet. Closing this does not stop the pump.

It is an annoying problem and I am almost ready to give up and buy a new pump. Working in this heat at the moment is not much fun. Thanks for your help

[Pib]

One last input/what-if, the "suction lift capability" on these types of pumps is only around 7 or 8 meters. Now if that "4 meters above the footer valve point" is more than 7 to 8 meters down the pump is going to struggle to suck enough water. The footer valve could be a 100 meters below the water level, but if that water level is not high enough the pump will not have the suction lift capability to suck in the water. With this current drought, well water levels have been dropping. Good luck.

Edited April 10, 2016 by Pib

[surat04]

One last input/what-if, the "suction lift capability" on these types of pumps is only around 7 or 8 meters. Now if that "4 meters above the footer valve point" is more than 7 to 8 meters down the pump is going to struggle to suck enough water. The footer valve could be a 100 meters below the water level, but if that water level is not high enough the pump will not have the suction lift capability to suck in the water. With this current drought, well water levels have been dropping. Good luck.

It worked like that for 8 years before this problem started.

[Pib]

One last input/what-if, the "suction lift capability" on these types of pumps is only around 7 or 8 meters. Now if that "4 meters above the footer valve point" is more than 7 to 8 meters down the pump is going to struggle to suck enough water. The footer valve could be a 100 meters below the water level, but if that water level is not high enough the pump will not have the suction lift capability to suck in the water. With this current drought, well water levels have been dropping. Good luck.

It worked like that for 8 years before this problem started.

Yea, if the water level has always been at least 4 meters above the footer valve then well water level is highly unlikely to be the problem.

But lets just say earlier/over the previous years the water surface level in the well had been higher than that 4 meters above the footer valve point. With the multiyear drought I expect most water levels use to be higher....in this drought I'm reading almost daily about dropping water table levels across the country. That would mean in years past with the higher water level the pump actually had a shorter suction lift distance...something within the max suction lift distance depth of around 7 to 8 meters for your pump. Note: I'm not sure about the exact suction lift max distance for this pump...it could be a little less than 7 to 8 meters...or maybe just a little more. Edit: second image below for the type of Mitsibitshi pump we have shows a max suction lift distance of 8 meters above well/underground tank surface water level.

Look at the image below at the suction lift distance diagram...notice the suction lift is measured from the water level surface (be it 4 meters or 400 meters above the footer valve) to the center of the pump...not from the footer valve to the center of the pump. And of course how much horizontal running pipe you have from the well to the pump is also a player in the max suction lift distance. Maybe to use an extreme example if you had a 1000 meter deep well, and the water level was 900 meters down but still 4 meters above the /footer valve (i.e., water level 896 meters down) that is far, far beyond the suction lift capability of your pump due to the low/deep water level.

But yes, if that water level of 4 meters above the footer valve has always been at the same depth then water supply is probably not causing the problem.

Edited April 10, 2016 by Pib

[surat04]

Water level to middle of pump should not be more than 5m.

[Pib]

You are good-to-go then on not exceeding the suction lift max of around 8 meters for the pump. Good hunting in tracking down your problem...simple water pump problems can sometimes not be so simple. Cheers.

[Crossy]

As someone mentioned earlier I suspect it may be the impeller, possibly combined with the level in the bore being a tad lower than normal due to the weather.

Many of the smaller pumps are peripheral pumps rather than centrifugal. These rely on a ribbed surface on the impeller which can wear (particularly if pumping water with particles in it) reducing flow and pressure. If your local pump shop has the spares it's a quick fix.

Otherwise get a new pump and order the parts, you can fix the dead pump at your leisure and have a spare for when the new one stops.

It's also worth getting a cheap multimeter to verify that the power supply isn't excessively low, anything lower than 210V for long periods needs investigating.

[wayned]

[HooHaa]

When I replaced the foot valve and input pipe I had to withdraw the old pipe from the well. It was wet 4 metres above the old foot valve. That's how I know there is enough water in the well. As previously said there is a shutoff valve on the pump outlet. Closing this does not stop the pump.

It is an annoying problem and I am almost ready to give up and buy a new pump. Working in this heat at the moment is not much fun. Thanks for your help

have you checked the pressure swtch? it is that grey cylinder about the size of a pill bottle at top of pump beside reservoir with priming cap. this has sorted the issue for me in the past. less than 100 baht to peplace i think and available at any good hardware shop that sells pumps

[Pib]

I would also buy a water pressure gauge (I bought mine at Global in the irrigation/pumping section for about 200 baht) to see what your output pressure "really is" versus perceived as being low....is it truly low....if it's truly low and not reaching your pump's pressure switch cutoff setting of around 1.8/1.9 bar the pump will continue to run. If it is reaching 1.9 bar and not cutting off well you need to relook your pressure switch, be it a new switch or not. Was the right switch for your model installed (lot of different switches with various cut on/cut off pressures? Your pump model pressure switch settings are 1.2/1.3 bar cut on, 1.8/1.9 bar cut off...settings are normally marked on the side of the switch protective cover. Was the switch manually adjusted?...there are one or two screws on the switch allowing adjustments....if these were adjusted without using a pressure gauge the cut on, cut off pressures settings could be set wrong...like the pressure cut off setting set too high...pump can never reach the cutoff pressure so it continues to run even with no water being drawn from taps or leaks somewhere.

With a pressure gauge you can check the actual output pressure and check if pressure switch is cutting off and on at the right pressure points...if it's reaching the switch output pressure cutoff but still not cutting off then than means your water input, impeller and other things are just fine.

Typical Pressure Switch on These Type Models (don't mess with adjustments unless you have a pressure gauge)

[surat04]

Packaging from the new switch. I didn't mess with it. Just installed straight out of the box.

[manfredtillmann]

I have had an old Mitsubishi 150 that was doing the same thing. The impeller in the pump was worn, most likely do to the high mineral content in the local water. The pump could never develop enough pressure to cause it to shut off. In the end I just bought a new pump.

agree, the most likely scenario given the symptoms the poster describes.

i did not manage to find tech. data on this pump but if it has a aluminum or plastic impeller these definitely wear out, particularly in low or high ph environments.

when you replace the pump go for a stainless steel impeller / housing type or a diaphragm version.

[surat04]

I now see on the label it says 150W but the pump is 100W could this be a problem.

[CGW]

Maybe? I would suspect that the pressure setting for a higher powered pump would be higher than for the lower model? try adjusting switch, you have nothing to lose now! will help if you have a Psi gauge.

[lopburi3]

Make very sure there is no power on pump before making any adjustments - switch sometimes only cuts neutral line and sections of pump will be hot - made that mistake long ago - and do not recommend it.

Worth the cost

Edited April 11, 2016 by lopburi3

[Pib]

I now see on the label it says 150W but the pump is 100W could this be a problem.

No..that is not a problem..it just means that switch can also handle up to a 150W pump which uses the same pressure setting.

[lopburi3]

But the cut in/out is not what is listed on spec for that model pump (but very close so should not be an issue).

Listed here as 1.3 and 1.9 rather than item shown at 1.1 and 1.8

http://www.jjpsupply.com/product/detail.php?id_product=7680