Potterton Puma 80 HW - OK, CH - will not start

[bigmike69]

Hi, HW is ok, CH won't start. Otherwise boiler is working ok. Serviced 2 months back. Suspect a possible diverter valve issue but want to run past some experts.

With the HW off, when the CH comes on the boiler does not fire up at all.

And with the the HW on, once the CH comes on the boiler powers down (to just pilot light).

If the water if off when the central heating comes on there is no effect to the boiler at all.

Does this sound like a diverter valve issue. It's a 12+ year old boiler but other than this I haven't had any problmes and it's well looked after.

I am in two minds whether I should investigate this, or replace the boiler (gas guy quoted approx 1250 for a new boiler and install - a newer potterton)

Thanks!

 

[45yearsagasman]

1st thing to check is that there are no dripping hot taps which will prevent the the wax capsule in the diverter valve from operating as is should.

 

[Agile]

The Puma is totally repairable.

I have not yet understood what you have written but with more time might be able to get a grip on it.

 

[Gasguru]

If the boiler is completely cold the burner should fire up the instant the CH is switched on via the room stat and timeclock. At this stage there is no reason to suspect the diverter.

AFAIK the only part obsolete on the Puma is the top socket type pilot burner.

 

[bigmike69]

Hi all, thanks for responses so far.

I read these forums before posting so all taps checked - no leaks, and i also bled all radiators (not much air came out). checked pressure of boiler also.


Agile, I spoke to you on the phone! What didn't you understand? HW works fine. When the CH is turned on it has no effect on the boiler, no click nothing.

And when the HW is on and then you turn the CH on it stops the burner and sits there idle with the pilot burning only. Most people who have diverter issues say the boiler comes on even slightly for say 20-30 seconds and then goes out but that doesn't occur in my case.

The clock seems to be working and the fact the HW goes off when the CH should come on indicates a signal is getting through to the boiler.

Thanks again and keep suggestions and thoughts coming as i will post the final resolution here.

 

[steve32]

I would be looking at the diverter valve.
The way we test diverter is turn heating off, turn on hot tap run approx 2 galls hot water, tap on slow so boiler fires and gets to max heat, turn off tap, pump on combi runs, when wax head in diverter valve reaches approx 80deg within approx 1 min hot flow to heating should get hot (if you hold the flow pipe be careful it will get very hot very quick) if pipe gets hot diverter is working if not then combi may overheat and go to lock out.


hope this helps

steve

 

[Agile]

Agile, I spoke to you on the phone! What didn't you understand? HW works fine. When the CH is turned on it has no effect on the boiler, no click nothing.

And when the HW is on and then you turn the CH on it stops the burner and sits there idle with the pilot burning only.

You did not put your location in your posting and I get a few calls from people with faulty boilers so there was no reason for me to associate the posting with your call.

You seem not to understand that HW delivery takes precedence over CH operation.

Tony

 

[ChrisR]

With the HW off, when the CH comes on the boiler does not fire up at all.

SO it's not a question of priority. It SHOULD fire, if the boiler's not HOT.

So I'd suspect a pcb fault.

 

[bigmike69]

steve - many thanks, useful info, will try that to see if the diverter is working.

tony, apologies i didn't expect you to relate me to the call.

chris - i think you might be onto something, is there ay way to confirm a pcb fault? as when the hw is on and the ch comes on it does send some signal to the boiler which shuts the hw heating off. (sorry i don't mean to keep repeating myself here!)

 

[ChrisR]

YOu're saying a signal sturns the heating off when he heating's on. What, the room stat?

If it's a pcb fault, it's very likely to be a joint failed or gone intermittent, or a sticky relay. No simple test apart from a replacement.
Often if you poke the board ( you don't have to be Corgi regd to do that ) you'll hear something like a spark or a relay click. The date will be on a sticker on the visible side of the board. If it's more than a few years, it's very likely to have failed!
I assume this is a Permanent Pilot version of the Puma and not the Electronic one - they have a second board.

 

[Agile]

He has already said its got a PP.