My old bathrooms website is here. Beware, it is an old site and I don't maintain it. Some of the info will be out of date.
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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 don't encounter the Promax very often, which is good because I don't like them. It's worse than that in fact, this is one of the few boilers I avoid working on whenever possible! In particular, I decline requests for me to service this Promax (or any of it's many variants) when workload is high. Firstly, like most condensing boilers, the combustion chamber seals MUST be replaced every time the combustion chamber front cover is removed, and few merchants stock this part. Secondly and more crucially, dismantling it 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 silicone method 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 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 condesnate drain. If I'm to service a Promax I fit new combustion chamber seals and usually a new combustion box base. This is EXPENSIVE and there are usually delays obtaining the parts, hence my reluctance to get involved. 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.... ;-)
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