Potterton Puma 80 combi

plumbingnovice · 6 Sep 2005

I moved into my new flat a few days ago where there is a Potterton Puma 80 combi installed.The flat was vacant for 3-4 months before I moved in so the boiler has\\\'nt been used for a while. (not sure if this is relevant)
My problem is after I have lit the pilot light following the instructions on the boiler (which fires up first time) and flick the switch from stand by to on, about 5-10 minutes or so later there is a loud banging and rattling noise and the pilot light goes out.
this happens whether I have the CH on or not.
The radiators are extremely hot but the hot water is intermittent, one minute cold, then red hot then cold again.
As the username suggests I am a bit of a plumbing & boiler maintenance novice so any advice would be greatly appreciated.
Three days after moving in I could do without spending a fortune.

Cheers.

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penpusher · 6 Sep 2005

Have you checked the system pressure guage which is situated on the bottom of the boiler on the left hand side (if memory serves), it should read 1 - 1.5 when the boiler is switched off?

plumbingnovice · 6 Sep 2005

Thanks for the quick response. Will check when I get home later. What if the pressure is higher or lower than 1-1.5? IS it easy to adjust?

penpusher · 6 Sep 2005

If the pressure is lower than 1 then you can adjust it. You need to locate the filling loop.

The filling loop is usually a silver braided pipe underneath the boiler (If the boiler is in the kitchen it'll usually be somewhere under the worktop just out of reach of any normal person!!) The golden rule is, if you're not sure GET SOMEONE IN WHO IS. I really can't stress that enough as my tenants try this and it usually ends up with 3 floors flooded out and a major repair bill!

If you can locate it, turn on the valve handles and you'll hear water enter the system, watch the guage until it reaches 1.5 then turn handles off. Now you need to bleed all your radiators and repeat as many times as necessary until all the air is out of the system.

Now turn on your boiler to CH and run the CH, the boiler may be noisy and/or lock-out (needing reset) but this should subside after about 10 minutes.

AGAIN, IF YOU ARE UNSURE DO NOT ATTEMPT IT.

Unlike gas and electric which have nice isolating valves/fuses, water is a real pain in the bum and can cause damage VERY quickly.

plumbingnovice · 6 Sep 2005

Will probably take your advice about getting an expert in. The kitchen is the only room in the flat that's finished. The slightest hint of a mess in there & i'll be in serious soapy bubble from my other half.
She has a bit of a sense of humour by pass where domestic disasters are concerned.

Many thanks for the advice.

penpusher · 6 Sep 2005

good luck to you, let us know how you get on.

gstens baxi · 6 Sep 2005

i would say ,from exprience, that it is one of 2 problems either the pump or diverter valve ,if not the pressure.

Agile · 7 Sep 2005

Might also be the DHW switch not switching off!

Tony Glazier

plumbingnovice · 7 Sep 2005

Tookyour advice penpusher. Checked pressure, it was approx 1.3 bar so left it alone. Bled radiators, quite a lot of air in them. (no flood or mess i'm pleased to report!)

Sysytem ran well for a while with just the CH on.

Tried running the HW, it was red hot and ran for longer than it had previously but a little while after turning the tap off the banging noises started again. Sounds like a kettle boiling followed by a 'clanking' noise. This is followed by a click where the pilot light goes out.

Does this point to one of the suggestions made i.e the pump, the diverter or the DHW switch?

Going to call in an expert but would like a little knowledge just to back me up.

kevplumb · 7 Sep 2005

dhw switch is fave probably sticking (as suggested)
large lump of brass lower left side
if it is sticking it wont let the boiler switch off and it overheats ans shuts the pilot off after a bit of banging and clattering

open the hot tap and see if the pin moves

plumbingnovice · 7 Sep 2005

Thanks for the tip. Will give it a try.

If the switch is sticking is it a case of cleaning it or is it a replacement job?

Excuse my ignorance

Timmo · 7 Sep 2005

Just a thought if the pump is slow or at the wrong speed it will eventaully overheat. check that the pump speed is on 3 otherwise. this is a very simple check otherwise continue with the advise you are recieving

ChrisR · 7 Sep 2005

Code:

open the hot tap and see if the pin moves 
[\code]
There's a red light on the pcb which comes on when water is being drawn, and off when it's not. If you release the front panel you can see it. (Instructions are here: [url]http://www.partsarena.com/baxi/[/url])

The flow switches can split their diaphragm, just get sticky, or the microswitch could need replacing.

This weather you can also tell if the HW flow switch is stuck on because the rads get hot (Leftmost pipe under the boiler is the first.) Then they just keep getting hotter until the boiler overheats and puts its own pilot out.

Agile · 8 Sep 2005

Unusually, nobody has mentioned the HW temperature sensor!

Whilst I cannot ever remember finding one failed, its a first think to check before getting involved in wet parts.

Tony Glazier

ChrisR · 8 Sep 2005

You get distinctly damp if you take it out! Fair enough though check its resistance which is...

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Potterton Puma 80 combi

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