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Potterton Promax SL, HE and HE Plus
Unusually for a condensing boiler, the Promax has a single, one-piece cast iron heat exchanger. (Most modern condensing boilers have single heat exchangers made from either cast aluminium or fabricated stainless steel. Those with a cast iron heat exchanger usually have a second, separate condensing heat exchanger.) Combustion arrangement is unusual too, with a modulating gas valve supplying a gas/air pre-mixing fan feeding an up-firing gauze burner. First stage heat exchange occurs above the burner, then the flue gases are routed to the back section of the heat exchanger where the condensing stage of flue gas cooling is carried out. Ignition is electronic, as with all condensing boilers. This means there is no pilot light running 24/7 wasting gas. I'm encountering the Promax more often these days, which is unfortunate because I don't like them. It's worse than that actually, it's one of the few boilers I avoid working on whenever possible. In fact I'm STILL being coy about it. It's on my (very) short list of boilers I am only prepared to maintain on a strict "no guarantee of any sort whatsoever" basis. In particular, I decline all requests for me to service the Promax (or any of it's many variants) and I only venture to repair a broken Promax if the customer accepts the repair will not benefit from a parts and labour guarantee, or any other sort of guarantee. I'd prefer really to completely decline all Promax repairs. Here are the problems: Firstly, like many older condensing boiler designs, the combustion chamber seals MUST be replaced every time the combustion chamber front cover is removed. Unfortunately few merchants stock this part and it will probably have to be ordered, with a wait of a day or two before the work can be completed. This part must be replaced every time the boiler receives it's annual service. Secondly, dismantling a Promax for servicing properly can lead to serious difficulty re-assembling it in a leak-tight manner in my personal experience. To service this boiler properly the aluminium combustion box base must be removed for cleaning. This part collects the acidic condensate and routes it to drain. Sadly, aluminium gets corroded by condensate and the joint seals usually get damaged too on removal too. Either a new combustion box base and seals are needed, or, the old one can be stuck back on with lashings of silicone bath sealant as a stop-gap fix to get the boiler running again. The plaster-it-up-with-silicone method also means the next engineer to service it has virtually no chance of removing the combustion box base for cleaning. This two factors lead to most street-wise engineers removing neither the combustion chamber front panel nor the combustion box base during a service. This means the boiler hasn't been serviced at all, just safety-checked and given a cosmetic hoover-out. As time goes by a breakdown becomes ever more imminent due to blockage of the condensate drain. To service a Promax properly it is essential to fit new combustion chamber seals and occasionally a new combustion box base and other seals. This is EXPENSIVE, there are usually delays obtaining the parts, and working on a condensate-corroded and possibly leaking boiler is never pleasant and if the corrosion causes more problems later, I tend to get the blame. Hence my reluctance to get involved with the Promax at all. My personal opinion is that this is a boiler well worth replacing if you have one. Apologies if this review page has turned into a bit of a rant.... ;-)
Page first published 14th March 2008 |
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