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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
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