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I had a new stainless steel tank fitted to my Mitsu water pump WP205Q, and since then the pump pulses, ie the water from the tap doesn't come out in a steady stream, but pulses. It's not enough to be a problem, but something has definitely changed and I'm not sure what. Before the pump only ran when the tap was turned on, and then in short intermittent bursts. I don't know if it's something that can be ignored or a sign of something breaking down. Advice appreciated.

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I think the tank is waterlogged. You need to drain the tank to get a blanket of air in it.

First, a pump connected directly to the mains is illegal (most of the world and some say Thailand as well).  You need a holding tank for proper pump supply to the house.

Close to 100% of homes that aren’t blocks of flats more than a 20 years old so around 95% of houses so hundreds or thousands of millions. 

2 minutes ago, ubonjoe said:

I think the tank is waterlogged. You need to drain the tank to get a blanket of air in it.

Thanks, will give that a try.

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Likely lost charge as ubon says. That or the diaphragm in new tank is dodgy. A leak somewhere (toilet cistern) or pressure switch issue could be other reasons, though unlikely if they were just working on it. Did they open the valve from the water tank? 😛

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I agree , or the tank cannot take air from outside ( unlikely , but idk the construction ) , or and this would be my highest chance , that is that the bladder tank of the pump is broken ( no need to replace pump , new air bladder tank is easy and cheap fix , my pump changed bladder tank after about 5-6 y of use ) . 

1 more option is possible , and that is dirt sticking somewhere in the pump . There is a drain valve somewhere in pressure side of pump which can be unscrewed and checked . Close all valves and shut down pump , unscrew that lid and open gently tank->pump and let some water drain from there , should be a steady stream non polluted . after you can check in house by opening also tap by tap ( unscrew the small filters in tap to check for dirt ) . If all is normal , reconnect everything again , and let air drain out of system .

Last 2 options , 1 i just thought about ... since it happened when changing tank , is the suction side of the pump to tank . Does it have a filter in the tank ? check... is the diameter ( smaller then before ? ) .

Last option , pressure switch broken ...

Does the pump shut down multiple times and start again , or does it just keep running but gives out discontinuous water ?

 

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2 hours ago, sezze said:

I agree , or the tank cannot take air from outside ( unlikely , but idk the construction ) , or and this would be my highest chance , that is that the bladder tank of the pump is broken ( no need to replace pump , new air bladder tank is easy and cheap fix , my pump changed bladder tank after about 5-6 y of use ) . 

1 more option is possible , and that is dirt sticking somewhere in the pump . There is a drain valve somewhere in pressure side of pump which can be unscrewed and checked . Close all valves and shut down pump , unscrew that lid and open gently tank->pump and let some water drain from there , should be a steady stream non polluted . after you can check in house by opening also tap by tap ( unscrew the small filters in tap to check for dirt ) . If all is normal , reconnect everything again , and let air drain out of system .

Last 2 options , 1 i just thought about ... since it happened when changing tank , is the suction side of the pump to tank . Does it have a filter in the tank ? check... is the diameter ( smaller then before ? ) .

Last option , pressure switch broken ...

Does the pump shut down multiple times and start again , or does it just keep running but gives out discontinuous water ?

 

The pump only runs when a tap is turned on, but it runs in short bursts, probably less than a second apart. Not sure if all the info you give is applicable to the Mitsu pump, or it could be it's just over my head. I wouldn't know where the pressure switch is located. The problem is finding someone who knows what they are doing, not the average Thai handyman who just hits it with a spanner and hopes for a result.

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I had the same problem, took a video & went to local repair shop & showed them. He reckoned pressure switch on it's way out. Bought a generic one (small wiring mods needed), changed out & works ok. This doesn't follow the best practice of fault finding, but I found it fixed the problem for a couple of hundred baht.

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2 hours ago, giddyup said:

The pump only runs when a tap is turned on, but it runs in short bursts, probably less than a second apart. Not sure if all the info you give is applicable to the Mitsu pump, or it could be it's just over my head. I wouldn't know where the pressure switch is located. The problem is finding someone who knows what they are doing, not the average Thai handyman who just hits it with a spanner and hopes for a result.

It is a fairly common problem so best to initially think there is no mechanical issue.

Close off the inlet, drain the outlet and close it up again. Open the inlet and let the pump fill and switch it on, should be ok. If the pump supply is below the pump you may need to fill the pump though the filler cap on the top, the finger type one, not the castle shaped one.

If the problem persists more likely to be a damaged diaphragm than the pressure switch, best to remove the pump and take it to a repair shop. Good luck.

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2 hours ago, tompelli said:

I had the same problem, took a video & went to local repair shop & showed them. He reckoned pressure switch on it's way out. Bought a generic one (small wiring mods needed), changed out & works ok. This doesn't follow the best practice of fault finding, but I found it fixed the problem for a couple of hundred baht.

The pressure switch has an operating range so the pulsing would be a bit slower than an air problem, that is very rapid, almost like a "chatter".

I have had to change a couple of pressure switches and found the same, wiring not quite the same, one was too short which was a real pain.

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3 hours ago, tompelli said:

I had the same problem, took a video & went to local repair shop & showed them. He reckoned pressure switch on it's way out. Bought a generic one (small wiring mods needed), changed out & works ok. This doesn't follow the best practice of fault finding, but I found it fixed the problem for a couple of hundred baht.

Looks like the pressure switch differential is set too close (maybe failing) have someone stand by the pump and listen to see if the pump starting and stopping. This would indicate the pressure switch is turning pump on and off 

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did they open the valve to the new tank? new tank shouldn't be waterlogged. pump pulsing seems to indicate your pressure switch is working fine. i would cocentrate on exactly what "they" did that changed everything.

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23 hours ago, giddyup said:

tap doesn't come out in a steady stream

But you did not mention that what you hear at the pump when a water tap is open. Water flow is not steady, how about the pump ? Does it turn on/off rapidly ? If it does, then the problem could be "pressure switch"

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43 minutes ago, whaleboneman said:

did they open the valve to the new tank? new tank shouldn't be waterlogged. pump pulsing seems to indicate your pressure switch is working fine. i would cocentrate on exactly what "they" did that changed everything.

AFAIK only changed the tank.

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5 minutes ago, The Theory said:

But you did not mention that what you hear at the pump when a water tap is open. Water flow is not steady, how about the pump ? Does it turn on/off rapidly ? If it does, then the problem could be "pressure switch"

Yes, I said the pump runs in bursts when the tap is open, about a second between "bursts".

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1 hour ago, kennw said:

Looks like the pressure switch differential is set too close (maybe failing) have someone stand by the pump and listen to see if the pump starting and stopping. This would indicate the pressure switch is turning pump on and off 

The pump starts and stops in bursts when a tap is open. I can stand right next to the pump and turn on a tap.

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I've had Mitsubishi W305Q (last letter changes with updates) and have had the surging problem a number of times.  The problem is adjustment.  Find a guy who knows what he's doing and he'll fix it in 15 minutes.  I guy who doesn't know may never fix it.  Once properly adjusted it should run OK for years.

Good luck,

Don

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On 5/25/2021 at 4:25 PM, ubonjoe said:

I think the tank is waterlogged. You need to drain the tank to get a blanket of air in it.

yes, that is analogous to the having a Resonator Box in the Intake for a fuel injection system (pretty rough running without one) 

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Posted (edited)

You should be able to simply unscrew the tank by hand (unplug the pump first).  Let it drain until empty and screw back on - just hand tighten.  Why a new tank would be waterlogged is another question - but that would be the first thing to try.

 

 

 

Edited by bankruatsteve
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  • 3 weeks later...

I am not sure if I have the same problem as you:

 

Our inline pump bringing water from the tank to the house just runs continuously. I have checked for open faucets/leaks to see what is causing it to run nonstop, but can't see anything. It seems to have a mind of its own now (7years old).

 

We just turn it on and off manually when we want to use water otherwise it will run nonstop and overheat.

 

I am not clued up about pumps. I have no idea what would cause a pump to behave irregularly.

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24 minutes ago, 2009 said:

Our inline pump bringing water from the tank to the house just runs continuously.

First thing to check is if the "bypass" is open.  IE: does your tank have water pumping in when the pump is on?

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25 minutes ago, bankruatsteve said:

First thing to check is if the "bypass" is open.  IE: does your tank have water pumping in when the pump is on?

 

Our well pump fills our tank and our inline pump brings water into the house.

 

The tank is usually full of water when our inline pump runs.

 

However, maybe on the odd occasion the tank has been empty (due to the well pump not coming on at that time) when our inline pump has been trying to suck water out.

 

I dunno if this answers your question.

 

This problem has been going on for weeks irrespective of whether or not the well pump is running at the time or how much water is in the tank. Not sure what started the problem. It happened randomly.

 

Maybe the inline pump is knackered?

 

 

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21 minutes ago, 2009 said:

I dunno if this answers your question

No. Is water pumping into the tank when your well pump is off and your "inline" pump is on? 

Edited by bankruatsteve
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1 hour ago, 2009 said:

Our inline pump bringing water from the tank to the house just runs continuously. I have checked for open faucets/leaks to see what is causing it to run nonstop, but can't see anything. It seems to have a mind of its own now (7years old).

Turn everything off, remove the pressure switch (3 screws). Lift up the spring and grommet, there is a rubber diaphragm which is probably perforated.

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Before ideas to fix @2009 pump, let's determine if it needs fixing. Obviously the pump is working if he gets water from an open tap and the pump is running. Also obvious is when the tap is closed and the pump continues to run non-stop, there is water being pumped somewhere. It's likely there is a valve open somewhere that should normally be closed. 

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1 hour ago, bankruatsteve said:

No. Is water pumping into the tank when your well pump is off and your "inline" pump is on? 

 

No water pumping into the tank when well pump is off.

 

Thank you

Edited by 2009
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43 minutes ago, bankruatsteve said:

Before ideas to fix @2009 pump, let's determine if it needs fixing. Obviously the pump is working if he gets water from an open tap and the pump is running. Also obvious is when the tap is closed and the pump continues to run non-stop, there is water being pumped somewhere. It's likely there is a valve open somewhere that should normally be closed. 

 

I have searched for an open valve but nothing is apparent. I wonder if a pipe has burst under the house or something.

 

Thanks

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16 minutes ago, 2009 said:

 

No water pumping into the tank when well pump is off.

Assume that is the same when the inline pump is on. Do you have a valve you can close at the inline pump output? Does that stop the pump? 

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