First of all, thanks for visiting.

I'm Mike Bryant, also known as Mike the Boilerman. This site specifically to help owners of Powermax boilers and/or technicians repairing them. Feedback I get from owners of Powermax boilers suggests they find the Powermax fiendishly difficult to get serviced and/or repaired. Heating engineers in general are very wary of them due to their chequered history and would rather avoid working on them whenever possible :-/

Anyway, this  page deals with the Range Powermax. If you have a Potterton Powermax HE then click the link in the column on the left. So I'll start with a brief description of the Powermax, why it is different from ordinary boilers, then more about the chequered history.... 

The Range Powermax was based on an excellent concept in my view - it's a shame the implementation was so flawed. The idea was conceived back in the days when mains pressure hot water cylinders were not permitted under the Building Regulations. The only way to get high performance showers was by installing pumps. The Range Powermax idea was to combine a boiler and hot water cylinder into one integrated device capable of delivering both central heating and mains pressure HOT water, by using the 'thermal store' principle, so high pressure showers could be fitted in flats especially without the use of expensive and noisy pumps.

A tank full of water was heated not by a separate gas boiler, but by an integrated gas burner that squirts flames down a number of tubes running straight through the water tank. The tubes heated the stored water which was then circulated around the radiators for central heating. But the best bit was the way mains pressure hot water was produced. Cold mains water was fed into a coil of tube suspended inside the heated water tank, and the cold water was heated through the wall of the coiled pipe in real time as it flowed through the coil on it's way to a hot tap or the shower. Mains pressure hot water at high flow rates with no pump, in full compliance with the Building Regulations of the day!

Now the problems...

1) The gas valve and burner gasket. The clever new type of gas valve does not take kindly to being fiddled with by technicians (or users) without the use of a flue gas analyser to measure the effect of the adjustments being made. Carbon monoxide can be produced in vast quantities. This problem combines perversely with the fact that the burner gasket is prone to leakage. A new gasket MUST be used every time the burner is removed for servicing according to Potterton-Baxi technical support. Few service engineers carry these burner gaskets in the van so I suspect few actually get replaced on servicing. The technicians who see no point in replacing the burner gasket are possibly the same technicians who do not carry a flue gas analyser, and CO from poor combustion leaking from the burner gasket has apparently lead to the deaths of a number of users of Range Powermax boilers. This is one reason for the dark reputation of the Powermax and the reluctance of technicians to work on them.

2) The aluminium flue. The Powermax twin-tube flue is very compact and is often installed running long distances across ceiling voids to outside. A poor standard of workmanship installing these flues can lead to the flues coming apart behind panels or boxing and flue gas discharging directly into living spaces. Should this happen on a conventional concentric boiler flue the outer air duct tends to suck the flue gases back into the boiler but not on the Powermax with it's pair of separate tubes. The Range Powermax is also very thermally efficient but not designed to be a condensing boiler. This high efficiency can lead to  condensation sometimes occurring  inside the flue duct. Not normally a problem except that the condensate generated is corrosive and eats through the aluminium wall of the flue duct in the long term. This is especially a problem on horizontal flue runs, and even more of a problem when the horizontal flue runs are concealed behind ceilings or boxing. The flue duct perforates and leaks products of combustion into the living space. Should poor combustion then occur, possibly due to incompetent adjustment of the gas valve, the user is at serious risk of CO poisoning.

These, as I understand it, are the two reasons for the poor safety reputation of the Powermax. Each individual model of Powermax also suffers from various other technical faults and failures just like any other boiler, but none of these other problems presents a serious safety risk provided any technicians working on the boiler have not been negligent.

Common faults and breakdowns:

1) Central heating failure while hot water continues to work as normal. The immediate cause is the central heating pump not running. The two common causes of this are timer/programmer failure and a seized or failed pump. The seized pump can be diagnosed by measuring for mains voltage on the input terminals. If voltage is present and the pump is not spinning, the pump needs freeing or replacing. If voltage is NOT present at the pump, check the programmer. This is notoriously unreliable. Testing for mains voltage on the output terminal of the central heating channel when heating is selected. No voltage means a new programmer is needed.
 

2) Hot water runs hot initially then cools down. Most commonly caused by a failed thermostatic blender valve. A new valve fixes the problem. Less commonly the cause can be water scale. If the Powermax has an external plate heat exchanger this can be replaced quite easily and hot water is immediately restored. Many Powermax boilers have an internal domestic water heat exchanger and chemical descaling will be necessary. Not especially difficult but time-consuming and invasive. Involves bringing chemicals, a descaling pump, hoses etc into your house.

3) Boiler refuses to light at all, showing the red lock-out light after three failed attempts to start. Several possible reasons for this, but the most common reason in my experience so far is a blocked automatic-air vent (sealed system versions only). The blocked AAV fails to allow accumulated air to escape from the collection chamber on top of the heat store and the water level switch inside the collection chamber disconnects the gas valve to protect the boiler from 'dry running'. Easily diagnosed by loosening the AAV. If air escapes from the thread and the boiler then lights, fit a new AAV! Next reason is very similar. The level switch inside the air collection chamber fails, ceases to detect the (correct) water level in the air collection chamber and disconnects the gas valve as above. A new level switch needs to be fitted. Third reason would be solenoid failure on the gas valve. The solenoid can be replaced on later (Sigma) gas valves but not on the early Ranco valves. A new gas valve will be needed. Other reasons for failure to light are usually control board failure or problems with ignition electrodes/leads. Both reasonably easy to fix. 

4) Random locking out. The user realises there is no hot water or heating, and the boiler is found to have locked out the with red light on. Re-setting the boiler makes it start again and run apparently perfectly normally but after a random period (hours or days) it locks out again, driving users (and their boiler technicians) to distraction. Firstly, the inlet gas pressure, gas valve settings and combustion settings all need to be checked and verified correct (specialist work) then if the fault persists, speculative parts-changing can begin. Changing the ignition electrode, ignition cable, gas valve and electronic control board in that order usually hits on an answer. These parts may be replaced serially to save money but multiple technician visits can be needed. Alternatively they can all be replaced in one visit at enormous cost for a more probable fix, but as with all intermittent faults, there is no certainty of a repair when the technician cannot reproduce and observe the fault occurring :-( 

5) Pressure gauge falls to zero then boiler locks out and refuses to start. Re-pressurising the boiler to 1.0 bar makes it run again but the problem returns after a few hours or days. A complex fault and a bit of a paradox because unlike many boilers, the Powermax does NOT have a pressure switch to turn the boiler OFF when pressure falls to zero! This fault is usually caused by a small volume of air accumulated in the air collection chamber in the top of the boiler. This air would normally be released through the AAV (auto air vent) but the AAV has stopped working. This leads to the level switch in the air collection chamber sensing low water level and disconnecting the gas valve leading to ignition failure and locking out. Re-pressurising the system compresses the trapped air, the water level in the air collection chamber rises slightly and the level switch senses this,  re-connects the gas valve and the boiler works again for a while. If the expansion vessel has also lost it's air charge (another common problem) the system pressure may then rise above 3.0 bar and the PRV (pressure relief valve) will let some water out of the system. The PRV will sometimes fail to fully close again and continue leaking water from the system until the pressure reaches zero, when the level switch will disconnect the gas valve. Re-pressurising makes it all work again and the cycle repeats. A new AAV and PRV and recharging/replacing the expansion vessel usually fixes the problem.  

6) A high-pitched whistle when running. A loud, steady, high-pitched whistle when alight, often audible from outside in the street, usually originates from the gas valve. Usually associated with the obsolete 'Ranco' brand gas valve and Potterton advise replacement of the valve, but other engineers report the problem can sometimes be fixed by adjusting the existing gas valve. Potterton advise replacement because adjustment needs special tools and getting it wrong can make the boiler dangerous. New gas valves are factory pre-set and need no adjustment after installation. Supposedly!

An expensive problem discovered on servicing earlier models is melted turbulators. The turbulators (long twisted stainless steel strips inserted into the vertical gas-ways through the heat store) overheat and fall down into the base of the boiler and are fiendishly difficult to remove. The sump cover underneath the boiler has to be removed and tough leather gloves worn to avoid the viciously sharp edges on the turbulators when pulling them out with brute force. The sump then needs to be replaced and resealed correctly (crucial for the boiler to operate safely) and new turbulators are then installed from the top. Then hope the same problem isn't found at the next bi-annual service!

I'll finish today by saying I live in Reading, Berkshire. Most of my work is in Berkshire, Hampshire, south Oxfordshire, Surrey and west London but if you are outside this area then I'm perfectly happy to visit. In fact I'll go anywhere! The only trouble with this is, from your point of view, is that I charge for all the time I spend repairing a boiler, and this includes the time spent travelling to and from site. This means the further you live from Reading the less economically viable it is to get me to visit. 

Alternatively I'm happy to give email advice to anyone wanting it, but not telephone advice. I had to stop that years ago when the weight of calls grew too great.

For my main site, check out www.miketheboilerman.com

Once again, thanks for visiting.

Mike Bryant, AKA Mike the Boilerman. 

First published 21/07/09
last updated 18/01/10