Stuart Turner single pump issue

[muggo]

I have a Stuart Turner U2.0 bar Single pump fitted to boost my hot water. It's about 10 years old but it's had the same problem from day 1 & ST aren't very helpful so I wonder if someone can advise.
Every hour or two, it bursts into life for a few seconds & then switches off.

I have hot water in a tank & an expansion tank in the roofspace. The HW tank takeoff is the one needed to avoid bubbles entering the system.

ST said I must have a leak as it's trying to pressurise the system. After searching everywhere for a leak or dripping tap, I told them there wasn't a leak. They sent me a new pressure cylinder (screws onto the top) but it made no difference. They then insisted I employ a plumber to write a report confirming there's no leak, which I did (at cost to me). They then sent an engineer to replace the pump.
Since then I've had the same problem. I fix it by removing the pressure cylinder (which is full of water) & fitting the spare one. I drain the full one & wait a couple of months for the issue to reoccur & repeat the temporary repair process. Neither cylinder can be pumped up at all (they need some pressure apparently).
I'm sure the issue is because the pressure cylinder can't be pressurised, but why do both cylinders behave like this? BTW I've tried several pumps.
Any suggestions please?

 

[Madrab]

Yes the expansion vessel needs pressure. The U2 is 0.9bar. Have you tried a pressure gauge on the vessel to check the pre-charge?

A universal pump will do exactly that, recharge the feed if it senses a pressure drop, it's how it works. Do you try to re-charge the vessel when it's on the pump, if so then it needs an outlet open or it wont re-charge, if you are trying it off the pump then it can only be a valve or hand pump issue. If the EV's are holding pressure then it has to be on the outlet pipework somewhere.

 

[muggo]

Yes the expansion vessel needs pressure. The U2 is 0.9bar. Have you tried a pressure gauge on the vessel to check the pre-charge?

A universal pump will do exactly that, recharge the feed if it senses a pressure drop, it's how it works. Do you try to re-charge the vessel when it's on the pump, if so then it needs an outlet open or it wont re-charge, if you are trying it off the pump then it can only be a valve or hand pump issue. If the EV's are holding pressure then it has to be on the outlet pipework somewhere.

Thanks very much Rob. I think you've solved the problem for me.
It seems the bicycle pump I was using to pre-charge the vessel wasn't up to the job plus I was trying to charge it when mounted. I took the spare vessel to my garage compressor & put 0.9 bar of air in it. Remounted it & all seems to be well. Time will tell!
A shame ST Tech Support or the user manual couldn't tell me the process in the first place...
Thanks again.
Cheers, Paul

 

[Madrab]

the user manual couldn't tell me the process in the first place...

ST U Manual

Section 11.2 ..... Page 30

That's for the monsoon but all the ST U-series across the range are the same

 

[muggo]

Yes the expansion vessel needs pressure. The U2 is 0.9bar. Have you tried a pressure gauge on the vessel to check the pre-charge?

A universal pump will do exactly that, recharge the feed if it senses a pressure drop, it's how it works. Do you try to re-charge the vessel when it's on the pump, if so then it needs an outlet open or it wont re-charge, if you are trying it off the pump then it can only be a valve or hand pump issue. If the EV's are holding pressure then it has to be on the outlet pipework somewhere.

Sorry to say that it hasn't solved the problem.
With no pressure in the vessel, it usually lasts a few weeks before it starts cycling again. After adding 0.9bar of pressure, it has lasted just a few hours before the problem re appears.
Let me stress again, there's no leak in the system.
Back to square one...

 

[Madrab]

Let me stress again, there's no leak in the system

I appreciate you thinking there isn't one @muggo but tbh with you there's really nothing else that it can be, it's atypical behaivour of a universal pump and a pressure drop and the pump's making it back up. it can be as simple as 1 or 2 drips on a tap, shower etc

The definitve test would be to disconnect the outlet of the pump from the distribution pipework, add a length of pipe with a tap/valve/gauge on it, run the pump and then shut the valve and leave it. You would see the pipe and gauge and can guarantee there's no leaks. If the pump runs without any drop then it's a problem with the pump, if it doesn't then it's out on the distribution pipework somewhere.

Alternatively disconnect the distribution pipework add a gauge and pressurise the pipework and do a pressure/leak test and leave it and see if there's a drop.

Only real way to know.

 

[muggo]

I appreciate you thinking there isn't one @muggo but tbh with you there's really nothing else that it can be, it's atypical behaivour of a universal pump and a pressure drop and the pump's making it back up. it can be as simple as 1 or 2 drips on a tap, shower etc

The definitve test would be to disconnect the outlet of the pump from the distribution pipework, add a length of pipe with a tap/valve/gauge on it, run the pump and then shut the valve and leave it. You would see the pipe and gauge and can guarantee there's no leaks. If the pump runs without any drop then it's a problem with the pump, if it doesn't then it's out on the distribution pipework somewhere.

Alternatively disconnect the distribution pipework add a gauge and pressurise the pipework and do a pressure/leak test and leave it and see if there's a drop.

Only real way to know.

Thanks again Rob. I can't fault your logic.
Is that perhaps why my ceiling's fallen in?

 

[just pumps]

Is there a non-return valve anywhere that is failing?

 

[muggo]

Is there a non-return valve anywhere that is failing?

I don't believe so. Where would one be fitted & for what purpose?

 

[Madrab]

Shower typically have NRV's fitted, stops cross/backflow

 

[Johntheo5]

Sorry to say that it hasn't solved the problem.
With no pressure in the vessel, it usually lasts a few weeks before it starts cycling again. After adding 0.9bar of pressure, it has lasted just a few hours before the problem re appears.
Let me stress again, there's no leak in the system.
Back to square one...

If your pump is equipped with these two isol valves then shut them and see how long it remains off.

 

[muggo]

If your pump is equipped with these two isol valves then shut them and see how long it remains off.

View attachment 278657

Thank you. Yes, I have those & will give it a go.

 

[muggo]

If your pump is equipped with these two isol valves then shut them and see how long it remains off.

View attachment 278657

I isolated those valves & the problem went away. Trouble is, so did my hot water supply.

 

[Johntheo5]

You just shut each a 1/4 turn and then reopened each by the same amount and now no HW when pump starts?.
Strange, maybe slacken HW hose at pump to check for air.

 

[muggo]

You just shut each a 1/4 turn and then reopened each by the same amount and now no HW when pump starts?.
Strange, maybe slacken HW hose at pump to check for air.

You suggested I shut them, which is what I did. When I opened them, the pump ran for 2 or 3 seconds. I didn't run the hot water with the valves closed - I just assumed with no pump in the circuit I'd be back to low pressure or none at all. Sorry for the confusion.