Common Boiler Faults
If you are having problems with your current
boiler and want to know whether or not it is worth replacing then have
a look at the list of common faults listed below for an idea of how serious
the fault may be. Repairs must be carried out by a Gas-Safe registered
engineer but the following information is intended to give you an idea
of the potential costs.
Replacement of parts
Boilers are identified by a Gas Gouncil (GC) number which is unique to
each model of boiler and consists of two digits, three digits and two
digits separated by hyphens eg. 47-063-04.
This can be found in the user manual or stamped on a plate attched to
Once you have the GC number you can search online for say, 'pump 47-047-33'
or 'fan 47-075-08' to get an idea of the price of the part you need.
A puddle of water under your boiler will either have come from
a leaky joint in pipework or from a faulty component. A
pipework leak is usually an easy fix whereas a leaking component will
almost certainly have to be replaced.
2. Low Water Pressure.
If your boiler has a pressure gauge on it and the pressure drops
below a certain level the boiler will not fire up. It
is normal for the pressure to drop over a long period of time - you should
have to top it up every three months or so. If you are having to do it
more often than this then you probably have a leak. First check the pressure
relief - a copper pipe which runs from the boiler to the outside
world, if water is dripping from this then the pressure relief
valve is faulty and it is a simple, inexpensive repair to replace it.
If the pressure relief is dry then the leak will either be in the radiator
pipework system or in the heat exchanger in the boiler. Small leaks can
be repaired by adding leak sealer to the system.
3. Noisy operation
Most boilers have two motorised components - the pump and the
fan. If the bearings on either of these wear out then they will get noisy,
the fan bearings are accessible and can often be oiled whereas the pump
can only be replaced.
In normal operation the pump starts before the fan so if the noise starts
as soon as the boiler turns on then it is probably the pump whereas if
you hear a humming first followed by the noise then it will be the fan.
Another source of noise can be a scale build up in the heat exchanger
which will then vibrate as water passes through it. The only solution
is to replace the part and unfortuantely they are never cheap.
4. Failure to light
First check the gas supply, prepayment meters are a major cause
of boilers failing to light. If your boiler has a fan and you can hear
that working then the air pressure switch (which checks the fan is ok)
may be faulty. If this is the case then the boiler will not spark, if
it does spark but not light then the gas valve or the circuit board need
to be checked.
5. Failure to stay
If the boiler fires up then the pump, fan and air pressure switch must
all be ok (barring intermittent faults).
The boiler may be overheating due to the heating system being clogged
with sludge, this can be fixed by flushing the radiators.
Faulty temperature sensors may be telling the boiler to turn off prematurely
and these can easily be checked with a multimeter.
6. Frozen Condensate Pipe
In extremeley cold weather it is possible for the drain pipe from a condensing
boiler to freeze which will stop the boiler working. The solution is to
pour hot water from a kettle over the pipe until it thaws. You may want
to consider re-routing the pipe to an indoor drain such as a sink trap
to reduce the chance of freezing.