Potterton Puma 100... End of my tether! To Replace or to Not Replace

[simon69]

I am coming to the end of my tether with this thing. The only reasons I have put off not replacing it is, other than cost, the fact that access is a bitch as its in a very tight cupboard in a small bathroom, and also the house its in is becoming flats in the near future (one year). After which I will need to redo all the bathrooms boiler and pipework anyway.

I have incessant problems with the pilot going out, the boiler cycling, and so on. When the heating comes on, it feels lukewarm anyway. I have bled all rads but they just don't seem to get that hot any more. Whereas, the circulating pump is boiling, as is the first bit of the flow pipe underneath, before the bypass.

I have had a loft conversion done which has extra rads in it now, so I wonder whether there is a problem with balancing, and whether I am asking a bit much of this boiler which would be better off in a flat itself rather than house with now five storeys. However we have come this far. Its just very annoying to have to check taps on various floors to try and work out why the house is stone cold when i come in.

I am debating whether to give the thing one last service, and have the heat exchanger replaced as well as maybe the PCB (or at least the Omron relays on it) as well as maybe the pump (which seems to be working fine but you never know), and the circulating pump, and the diverter valve (and the stats? And so on!)

I just wonder, even though the water that comes out of the pump and the rads is nice and clear, whether the pipes and/or the heat exchanger are a bit blocked and the system just needs a flush.

If I do replace it, what combi could take a big house with dozens of rads in it (two basement six ground floor six first floor four second floor two loft!) like this one can??

Any thoughts welcome.

 

[jackthom]

How far is the very hot flow water getting? You mentioned a bypass, is it possible the majority of it is going that way and not through the radiators?

Sounds like the boiler is producing some nice hot water but there's either not enough flow, a short circuit through the bypass, or both.

 

[simon69]

when its stuck it doesnt get further than the flow pipe just below, neither to the bypass nor to the rest of the system. When it does work, it goes everywhere, then its just a lottery to see which rads get properly hot or not. I've raised the pressure up a bit to 1.75 to see if that helps. The bypass never gets hot unless the rest of it does too so i don't think there's a bypass problem. I seem to have a nasty combination of a short cycling boiler and a set of fluctuating rads that get hot when they feel like it. Which to me makes me think my heat exchanger is compromised ... ?

 

[Agile]

Your problem will be the diverter valve element.

Not impossible but somewhat difficult to get.

Your boiler gives 24 kW which means it can heat about 24 not too big rads.

Your posting is a little vague about flats etc.

But calculating the heat loss of the property is something you could do for fun. A combi like yours is sized on the hot water requirement and not the heating which is always lower.

A five bed detached house is usually about 18 kW if reasonably well insulated. To the latest building regs usually less than 10 kW.

Tony

 

[jackthom]

deleted

 

[simon69]

Hi Tony

Many thanks for your reply. Do you mean difficult to get at? I can see on ebay the caspule for £20 or the whole assembly for £60. Shall I just swap out the whole thing rather than fiddling around with the capsule?

Certainly the pilot going out after someone running the hot tap makes me think I need to do this for sure.

Simon

 

[Agile]

The pilot going out is likely to be an overheating problem. Or a gas/combustion issue which we don't advise on here. Not necessarily so easy to diagnose why. But could indicate sludge in the main HE. But that could be cleaned with chemical treatment.

The official wax capsule is obsolete. Those you see are probably manufactured for TRVs or possibly copied in India. They are usually fairly easy to change. But on one version of the diverter valve it is very difficult.

The official price for a full diverter valve is about £140. But on Ebay you get some less than kosher suppliers.

Removing the whole diverter is quite difficult unless you know the engineer's trick.

Tony

 

[ianmcd]

firstly make sure that you dont have any dripping HW taps, doesnt take much on these to cause the symtoms you are getting, changing the whole valve is a pain and very seldom needed, just change the wax capsule if you can get it.

that is the part you need justtake your time when fitting it you can get it wrong but it isnt a hard job .

http://www.ebay.co.uk/itm/Potterton...247088?hash=item4ad52f9c30:g:P0wAAOxyc2pTcO66