I have a Halstead Best 60 boiler which is less than two year's old and
has suddenly stopped functioning. Initial investigations showed that
the 2A inline fuse had blown. Replacing this has got the pump going
again but the boiler still fails at the first hurdle i.e. the fan does
does not start. Working throught the troubleshooting chart in the
manual, I got to the point where pin 1 of the ignition control
connector was not showing 10vdc. On the strength of this, I have
replaced the thermistor and Aquastat PCB but am now no further
forward. The connector still shows only 2vdc when the connector is
disconnected and 0vdc when connected.
I am now confused. Either the replacement PCB is also faulty or the
problem actually lies in the ignition assembly PCB, the only other
likely, major (and expensive) component left. I might also mention
that the ignition lockout light started coming on regularly during the
summer but seemed to settle down again in the colder weather. Does
anyone have experience with this type of boiler please.
When working through the diagnosis charts it is well to keep in mind that
not every outcome is listed as a possible end point (at least IME).
The fuse having blown (is this 230V stuff or low voltage?).
If mains it might be an intermittent earth fault on the pump or perhaps
the fan motor.
Almost all 'modern' boilers follow much the same sequence of operations.
1) Demand sensed. Usually 230V in or a pair of connections made. Or water
flow on combi.
2) Various 'hard' switches need to be OK - low water pressure, over heat etc.
3) Start Fan and Pump (fuse blows at this point maybe).
4) Detect air flow maybe also water flow (i.e. pump+water) OK.
5) Open gas valve (at ignition rate) or pilot gas valve. Start sparker.
6) Detect the flame and go to full rate or open main valve. Stop sparking.
7) No flame - perhaps try gas valve and sparker again or lockout.
My guess is that maybe you have a dodgy fan that is broken and
perhaps shorted out when dying?
Perhaps the 'Pin 1' gets 10VDC when the air pressure switch closes?
I would like to get all this down into a FAQ to do for boilers what
'Silcon' Sam Goldwasser has done for all things electr(tron)ic.
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Many thanks for that.
It was a 230v fuse and this has not blown again since replacing it. In
your sequence of operations, demand is sensed correctly and starts the
pump via a connection through the boiler. There is an overheat sensor
which checks out OK and the thermistor also checks out (1 meg ohm at
room temperature, reducing with temperature rise). The sequence stops
where the fan fails to start.
I am very pleased to say that, in the meantime, I have had a response
from Halstead technical services. They say that, if this fuse goes, it
is usually something external, perhaps a power surge or one of the
other causes you mention. The probability is that it is the ignition
PCB which is faulty so I am now giving this a go.
Will keep you posted of the outcome.
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