My combi has been installed for 8 years, Has been serviced every year
since and never been any prob until now. Central heating works fine
but hot water giving problems, it comes on fine when hot water tap
turned on, runs hot for approx 1 min then gas goes off and water runs
cold, if left running it will come on again after a few mins but
again swithches the gas off. you can hear boiler close down. Have had
main circuit board changed, sensors and thermostat changed,pump
changed with no avail. The engineer carrying out the repair is
starting to run out of ideas. I suggested that boiler may be sludged
up or have deposits as I live in hard water area and was overheating,
this was poo pooed, I dont suppose they like an amatuer telling them
in case I am correct. I suugested a complete new boiler but they
insist it can be fixed as boiler is in very good condition. This is
costing a bloody fortune £275 to date and still no further forward. Oh
I tell a lie there,I now have no hot water at all.They are coming back
tomorrow for a 3rd attempt. HELP before I have to remortgage to
repair this boiler.
Do either you or your boiler bod have the boiler manual?
The LED sequence is very useful in isolating the cause of problems
If you don't, I can make a copy of the relevant bits, but I would need
to know which main board you have. There are two, the 404S656 (which has
6 LEDs in a line) and the 404C147 (which has the LEDs dotted around the
If you want to ring me at work, I'll see what I can do. Contact details
are on the website - www.cetltd.com
On Sun, 07 Dec 2003 15:06:57 +0000, Bill Riichardson wrote:
Almost certainly you need to descale the secondary heat exhcnager.
The boiler just can't get enough heat into the HW through the chalk and so
If you have a HW temperture control you might be able to turn it down
and get the boiler to make a much smaller quantitiy of HW without cycling
the flame on and off.
Incidently since the CH works fine there was never any good reason to
change the pump, was there? Though sensors, thermostats and PCBs were all
_possibilities_ which have now been eliminated.
If possible try to get the temperature of the primary water measured
just before the gas cuts - this should be around 80C +.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
it was the air flow sensor (which is two temperature dependent resistors
in a housing)
The fitter battled on, determined to fix the problem and didn't charge
above the quoted price to fix it, despite spending well over a day
getting it sorted. Well done that man
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