Fix or replace failing water pump

[SantiSuk]

My standard domestic Mitsubishi water pump has been playing up badly. It was taking several minutes to respond (by switching on) to a 'water request' (the opening of a tap), sometimes not delivering good pressure thereafter and running on for 20 minutes after the water request was stopped (tap closing).

I gained the impression that the pump in running on was overheating and shutting down when it got hot.

Water pressure to the taps was improved significantly by following guidance elsewhere on the DIY forum to open the plug on the pump tank (with due care - it did explode!), drain the pump tank and restart.

However, the pump is still not switching off and will now grind on and on for hours.

My question is whether the clearly replaceable part that is screwed into pumping mechanism (pictured) has a part to play in the switch-off routine and whether it is worth replacing that. Or should I just buy a replacement pump. The pressure has built up over the last couple of days following the 'air bleeding exercise' to an extent that the gaskets seem to be blowing and water is jetting out in a small rivulet.

I could take it down the local pump shop for an overhaul but I suspect they would hang onto it too long waiting for parts.

If anyone does think that part is a switch/regulator that is worth replacing then what is the caution that is printed on its body (a cross printed on a picture of the screwdriver unscrewing it - is it no more than a caution to relieve pressure in the pump tank first before unscrewing?

[chiang mai]

That's a pressure switch, readily available almost everywhere here and cheap and simple to install - it's the device that sense water demand/supply when a tap is opened.

[Crossy]

Yup ^^^, pressure switch.

It also has an adjustment so you can reduce the trip pressure so it turns off. The caution is not to adjust it

TAKE CARE the metalwork inside the unit may be live!

Run the pump with the taps closed (make sure you have water pressure at the taps then close them).

Slowly turn the adjustment towards the "-" symbol, the pump should stop.

Open a tap, pump should start.

If that doesn't result in the pump working properly then a new switch may be needed, but it's also possible that the pump itself is worn and not developing enough pressure (if you're seeing leakage at the seals that's a strong possibility).

Time for a replacement pump I suspect, although service kits are available can you survive without whilst it's fixed?

[lopburi3]

Go to local pump shop - have them send someone to repair - they will do onsite and the cost is a lot less than loss of your life. If you must work on it make very sure power is off (and that means both hot and neutral electric lines are cut - not a problem if you still have a plug than can be removed but if wired into a switch they are often a real danger - let someone aware of the danger take care of the problem - they actually know what they are doing in most cases as this is a common problem - I know we hate to pay for service people but for something like this you are providing a service to the worker and he is providing a service to you and it is not at the costs we may expect/fear.

[canuckamuck]

Also consider if you have a leak. The pump going on and on might be because it can't pressure up.

And it wouldn't hurt to drain the pressure tank again either.

[Pib]

Yes, these pumps are easily repaired. I've personally replaced the pressure switch and air balance control valve on mine.

Have a water pump shop/tech fix it for you....will be a lot cheaper than a new pump. A generic pressure switch for your pump costs approx Bt250 (I bought a spare at local Amorn Electronic store)...and I have also replaced it before with a genuine Mitsubitshi swithc which costs approx Bt750.

And yes, as long as you don't have a water leak somewhere that's really the cause behind the pump continuing to run, your problem is probably the pressure switch contacts have fused together not allowing it to disconnect. This will cause the pump to run & fun until the motor's built-in thermal relay trips to shut the pump off. After about 30 minutes the thermal relay will automatically reset itself and once again the cycle continues....pump runs until it overheats...then the thermal relay trips....etc...etc....etc. This is what happened when I had to replace my pressure switch...the switch was around 5 years old.

[SantiSuk]

Thanks everyone. Will see if local shop will send someone, though the unit is plugged in with a standard 2-pin rather than wired in to a box, so I'm unlikely to kill myself. Yes I had figured that a leak might explain the lack of switch on pressure but I can't find one unless it's in the clay between pump room and house (the house has accees underneath so i can see a lot of the supply pipes. Also I clearly have a lot of pressure latent in the system afyter the pump has ground (grinded?) away.

I could easily have done serious eye damage however the second time I drained/bled the air tank. The air tank drainage plug shot off with such force, narrowly missing my head. That's because the second time I did it I had turned off inlet and outlet valves and must have stored all the pent-up pressure in the tank. If I had to do again I would adopt the routine I first used which was to close the inlet supply to the pump but keep the outlet (pump to house) open; there was only a minor pressure pop from the drainage plug that time; mind you, the water ran and ran back down from the house and when I finally decided the water had run enough I closed the drainage plug and re-ran. Pressure never really got up to snuff that first time, whereas second time it certainly did. Lesson is I think to close the valve on the water supply (in my case tower) side but keep the valve on the house side open before opening the air tank drain (perhaps run taps in house first too to reduce pressure) then close the valve between house and pump once the air tank drainage plug has been removed, so that no more water drains back into the pump air tank. Just a thought to save any other 'bleeders' a potential unexpected bleed.

[chiang mai]

I had a very similar problem and it took me forever to find the leak, turns out it was a blue pipe joint and was barely noticeable but still there nevertheless - it doesn't take much.

[canuckamuck]

If it is possible for you to shut off the water to the house after the pump, then you have a sure way to know if the pump is running on because of a leak or whether it is a problem with the pump. Just close it and run the pump and see if it shuts off in a timely manner.

[Pib]

If it is possible for you to shut off the water to the house after the pump, then you have a sure way to know if the pump is running on because of a leak or whether it is a problem with the pump. Just close it and run the pump and see if it shuts off in a timely manner.

As canuckamuck said, it's good to have a shut off valve right after the pump outlet. And also have a shutoff valve(s) on the pump inlet side from your water sources(s). This way you can completely isolate the pump from any outlet or inlet issues possibly causing a problem....like making you think it's a pump problem when actually it's not.

[Pib]

Also regarding the pressure switch, depending on it's design you may be able to see the electrical contacts through some side holes with the cover removed. You could on my original Mitsubishi switch and even the spare generic I have.

When my original switch failed with the contacts fusing together I was able to get them apart easily and then used a burnishing file to clean off the carbon on the contacts which was causing them to fuse/freeze together. The contacts cleaned up well although after the cleaning the contacts combined with 5 years of use the contacts were wore down a good amount--but still operational. I fully expect the switch would have worked just fine for a couple more years but I had already installed a new switched and later bought a new generic switch as a "new" spare. But actually counting my original cleaned/fixed switch, I now have two spares....with two spares I expect the current switch will never break as I'm sure that's one of Murphy's Laws.

[SantiSuk]

So the screwdriver warning on the pressure valve (the picture was of a spare one I seem to still have from an earlier less powerful pump that was replaced on installing a swimming pool) is an electrical concern warning about disconnecting/grounding is it?

I did close the outlet valve this morning and the pump still grinds, so likely a pump/regulator fault, not a pipe leak Canuckamuck. Yes I do have valves to both inlet and outlet sides of the pump, which is v useful for bleeding water out of the tank.

I briefly celebrated Crossy's advice when the pump did cut-out on turning the pressure/switch body, but I was unable to find a position that repeats the trick on a day-to-day working basis. Local village water pump man (motorbike mechanic who turns his hand to all motors!) has now turned up and confidently opined that he can fix the leak and will replace the switch. If that doesn't work it's down to the Amphur pump shop to see how long they would take to investigate and if possible recon the pump (since it looks pretty easy to disconnect). If still no joy, then it's down to the big city Watsadus for a new one (but giving the local shop a chance to bid against watsadu price plus diesel/my time, to pick up on the 'support-a-local' theme posited by Lopburi3. With meuang Ubon being 85 km away that gives them a 1,000 baht shot (make it 2,000 - my time is precious, since I go to the UK for an annoying one week visit in 3 days time and it's a 3 hour round trip) as a price differential.

[kamalabob2]

SantiSuk:How did your quest to repair or replace your water pump end up? For the past 10 years I have used the services of a local water pump shop which would send a repair service technician to my home in a small town 40 minutes from Buriram to install or repair my swimming pool filter pump, Mitsubishi and Hitachi house water pumps. The same store had a team of repair men to install and service a submersible Franklin Schaefer well pump in a village home about 35 minutes from Buriram. There must be similar high volume water pump shops in other provinces in Thailand that are the top seller of Mitsubishi water pumps. I noted a Hitachi Promotional woman who posed for photos in the repair department of this Isaan water pump shop.

[Pib]

Look at the grin on his face....repairing pumps must be an enjoyable job.