In message .uk, Ed
Sirett writes
On Sat, 22 Jan 2005 02:43:49 -0800, Peter Dron wrote:

I could do with some help re a Baxi Solo 50pf. Some mornings we are
getting up to a cool house The boiler has come on the time clock
an obviously run for a while but then stopped working: The "boiler
on" light is on and the pump running but nothing more. It almost seems
as if it is in "cool down" before going off. Various options to get
it going again: Turn off the power to the boiler and then back on -
reset the overheat and off it goes. Or turn down the room stat till
it clicks off and the change over valve operates sometimes restarts it
as does turning down the boiler stat potentiometer until off; pause;
back on.

Also secondary simptoms: sometimes when cycling correctly, on the
boiler stat, the boiler fires up and immediately shuts off, fires up
again,off, fires up and runs.

From my own electrical/electronic experience over many years I suspect
a pcb problem, a relay or poor contact somewhere but would welcome
others thoughts.

These would typically be the symptoms of a failure of flame failure
sensing.

Either the gas is not really being lit and then the PCB doing its stuff
just fine, or the gas is lit but the flame sense probe and/or pcb is not
seeing the flames.

Check the ignition and flame sense wiring and electrode positions first
the pcb last.

By which he means (in layman's terms)

Check that the HT lead is intact and has not broken, especially at one
of the connectors (the insulation is also crimped, so it's not always
obvious that it's broken

Check that the electrode is actually in the pilot flame and has not
corroded and burned away

lastly, I would add, ensure that the earthing is good - no resistance
(less than an ohm) from the electrode earth to the pcb and the main
earth
--
geoff