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Powermax Repairs by Mike the Boilerman - Gas Safe Registered technician covering areas within driving distance of Hungerford, Berkshire. Call or text me on: 07866 766364

Powermax HE by Potterton

Before you read too much of this page, please not I no longer repair this specific version of the Powermax, the Powermax HE. I keep the page here as it might help you or your gas technician. 

Despite sharing a name, the Potterton Powermax HE is about as  different from the old Range Powermax as it is possible to be (and consequently suffers from a completely different set of problems). The main differences are that  HE is a now condensing boiler ('HE' stands for 'high efficiency'), and is no longer a thermal store. Instead it is a plain vanilla gas boiler and a small but conventional mains pressure hot water cylinder all squeezed into a single box. 

It's a shame that Potterton chose to keep the name 'Powermax' for this appliance because it means owners still find difficulty in getting a gas technician to attend because as soon as the word 'Powermax' enters the conversation, the gas bod switches off and loses interest due to the poor reputation of the preceding Range Powermax. 

This appliance is actually quite a good piece of kit in my opinion. Most of the problems they exhibit seem to be associated with system pressure loss which is not always a fault in the boiler - leaking pipework or radiators can just as easily be the cause. But not always! Here are the problems I regularly encounter with the Potterton Powermax HE:

1) A hard-to-find leak, causing water marks and/or dampness on the floor or ceiling below. Early versions of HE has a rather thin aluminium casting at the back of the heat exchanger to collect flue gases and condensate. So thin in fact that the flue gas condensate tends to corrode through it and leak out at the back of the boiler. This is potentially very dangerous as flue gas leaks out through the same hole into the house and it needs fixing immediately. It's a difficult repair because the boiler part needs to be completely dismantled and the heat exchanger removed to gain access to the failed casting. Potterton are rumoured to come out and fix this fault free of charge even when the appliance is long out of guarantee due to the potentially serious consequences of this fault. when they hear of an instance of it. (Ok it's not a rumour, an employee at Baxi-Potterton told me this!) Later versions of the HE were built with a much thicker and more robust casting.

2) An easy-to-find leak. It's probably the heating bypass valve, just behind the front panel. It's adjustable. It's just 'there' at the front and very tempting to both DIYers and gas technicians to idly adjust. BAD MOVE, because once disturbed it will leak for ever more. The only fix it to order and fit a new bypass valve. Of course a far easier fix is to not touch it in the first place :-) Now you know, but probably too late or you wouldn't be reading this.

3) User LED display is blank and the boiler is lifeless and won't start. It's as though the mains electricity to the boiler is switched off but you've checked and it isn't. This is typically control panel failure. A fiendishly expensive part but replacement is necessary UNLESS one or both of the surge protection fuses on the board happen to have blown - check them first. New fuses 'could' save you a load of money! (Fuse info supplied by James - many thanks James). Few merchants keep the control panel in stock should the fuses be fine on your dead board so it usually has to be ordered directly from Baxi-Potterton. The repair can then be complicated by the fact that the pressure sensor was upgraded and old pressure sensor may be incompatible with the new board and needs replacing too. Yes you've guessed, it will have to be ordered as it's a special order component. Once you have obtained the new, compatible sensor you will then find the connection cable is different as well so it won't plug in, and a new cable also has to be ordered as a special part from Baxi-Potterton. The whole process can take up to a month. Can you guess how I know this? Fortunately my customer had a second home to go to but the whole episode made me look rather incompetent. Huh.

4) Boiler won't start, with error message A15 showing on the user display. This is low system pressure. The immediate fix is to find the filling loop and turn it on for a few seconds to raise the system pressure back to the optimum range of 1 to 2 bar. Trouble with this fix is that the fault will usually return after a few minutes/hours/days because the reason for the original fall in pressure has not been found and addressed. There will either be a leak on the radiator circuit OR the water will be escaping through the pressure relief valve (PRV) in the boiler. PRVs are notorious for letting water by. They do it when crud (well-known technical term in the industry) gets stuck in the valve seat. Crud only gets in the valve seat if the valve opens in the first place. The valve only opens in the first place if the pressure in the system gets too high. The system pressure gets too high if the expansion vessel stops working. The expansion vessel stops working when it loses the nitrogen charge it came with from the factory. This is supposed to be checked each year during the annual service (you DID have it serviced didn't you?) Even if you did, most service engineers don't bother checking it because it is a faff to measure.... anyway I'm stopping describing this fault now because I'm bored with it. I hope you understand - you probably get my drift by now anyway... :-) Ok, fitting a new PRV and re-charging the expansion vessel usually fixes this one. Although half the time a new expansion vessel is needed on these...

5) User realises the boiler has stopped working and it has locked out showing the A01 error message. Pressing the reset button makes it start apparently normally but the cycle repeats an hour, a day or a week later. No technician called to attend can ever find anything wrong. Unfortunately I've yet to encounter this problem personally on a Powermax HE so I have no experience of how to fix it but I DO however get this exact problem from time to time on my Keston C25! I'm reasonably certain both boilers use the same gas valve. The settings on my Keston gas valve tend to drift out of adjustment over time, so the first thing I'd try on a Powermax HE with this problem would be to check the combustion settings using a combustion gas analyser and adjust if necessary. The Powermax HE manual also suggests cleaning/replacing the ionisation probe and lead.

6) Random lockouts with the boiler displaying the undocumented error message A02. Irritatingly, the instruction manual does not list A02 as a possible error message, so I called Potterton technical support this morning for some information. It turns out this is an error message displayed on early versions of the Powermax HE which have Version 1 control boards. It is caused by high resistance or poor circulation in the radiator circuit. The most common cause of this is all the TRVs closing down as the house approaches being warm on a system with no bypass circuit having being fitted by the original installers. A bypass circuit is needed to allow some water circulation when all the TRVs (thermostatic radiator valves) are closed. I'm told board versions 1A and 1B have different software and will not lock out the boiler with error code A02 even if circulation is poor. The simple fix is to leave one radiator permanently fully ON. If this makes no difference then a new control board will be needed. Best to make sure its a v1A or v1B control board. The version is marked on the board.


I’m afraid I no longer work on the HE version of the Powermax. I maintain this page for reference only. If you have one, my best advice is to replace it. These are troublesome boilers.

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Copyright MICHAEL BRYANT 2020

First created 21st July 2009

Last updated 10th May 2021

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CIPHE registration number 56207

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