Blowing hot and cold


Postby Vincenze » Sun May 10, 2009 10:32 am

My Potterton Puma 80e is over 10 yrs old and a solid (and big) old boiler that has served my house well.

It provides hot water pretty well throughout the house, although I would say that there have been hot ans scalding issues in the downstairs (Aqualisa - Aquarian mixer). I have a PRV set at 3bar for supply in to the house.

But I have an upstair's thermo mixer shower that cycles between hot and cold. When the shower is left on I checked the pilot and flame-up and see that it clicks on for a while then goes off. The upstairs basin hot tap (in the same bathroom as shower) provides consistent supply of hot water.

I am wondering if this is a flow issue to the shower upstairs. Any remedies?

Thank you – Vince
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Postby htg engineer » Sun May 10, 2009 2:45 pm

Probably, if the heat isn't getting away from the boiler - the flames will go out - when the temperature drops it will come back on - causing the hot/cold issue.

The hot is probably restricted quite abit, if the water is too hot the shower is mixing it with cold. Try turning the boiler stat DHW down so that the water coming out of the shower is more from the boiler and less from the cold mains - the boiler shouldn't go off as often - if at all.

Ideally set the boiler stat to a temperature that is suitable to shower and wash in, that way all the water will come from the boiler and none or very little from the cold water supply - it'll still be good pressure and the heat will get away from the boiler quickly.

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Postby Vincenze » Sun May 10, 2009 6:32 pm

I gave it a try: turning down the boiler water heat control (not the central heating one).

But it still flames up for 3 minutes and then goes back to pilot for 5 mins – and so on. From the basin hot tap in the same bathroom I get a consistent supply of hot, although occasionally it does go cold temporarily.

It must be the mixer holding up the hot water and tripping the cut out.

If I were to get a boiler to replace it would I be guaranteed to solve the problem, I wonder? How long can a Potterton last for? It has done a 12 yr tour of duty. What Btu and boiler type would anyone recommend for a 3 bed semi with 2 showers?

Is a mains PRV set to 3bar too low? And I did move it once so I don't know if it is exactly on 3bar because there is no meter.

Thanks htg for your time.

Vince
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Postby rosebery » Sun May 10, 2009 9:22 pm

@ HE

Could this be possibly a boiler temperature sensor problem?

Cheers
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Postby htg engineer » Mon May 11, 2009 3:37 pm

It could be a sensor problem or a partial blockage in the heat-ex, as the Puma doesn't have a plate heat-ex the hot water is heated directly by the flames through the main heat exchanger and they do scale up badly - but you would expect to have this problem with all taps - unless the flow rate at the other taps is greater.

It's hard to say if a new boiler would solve the problem - as the problem doesn't really seem to be with the boiler as the other taps are fine - more with the flow rate thorugh the mixer shower ?


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Postby Vincenze » Wed May 13, 2009 5:48 pm

I might try a new shower head that has a greater flow rate. Is that daft?

There could be a sensor problem because even the normal taps do fluctuate, but over longer periods of time.
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