In message , Ed Sirett
writes
On Tue, 01 Apr 2008 22:19:21 +0100, Andy Hall wrote:

On 2008-04-01 21:32:49 +0100, geoff said:

In message
,
" writes
Hi all

I have an Ideal Classic conventional boiler, approx 13 years old. The
CH system is the type having a header tank in the loft. Over the past
few days, it was making a whistling noise and was taking a long time
to fire up (10 to 20 minutes from when it was turned on at the
controller). Today it does not fire up at all, and it makes a fairly
quiet humming noise when the controller is asking for heat. Any ideas?

Is the fan turning ?

Is there a spark clicking away ?

You need to discover at what point in the sequence it's failing

call for heat
if temp sensor considers it's cool and O/H stat is short circuit
fan comes on
this transfers the air pressure switch which tells the pcb to
a) spark and
b) open the pilot valve
pcb senses the pilot is alight
pcb opens the main valve

Is that how they still work?

I had a Potterton wall mounted job in the 70s that worked like that. The
spark generator became class F, but I was able to figure out what was
happening. Other than that, it was quite a good boiler.

That would be fairly typical of a 'Middle-tech boiler'
The Potterton Profile would be like that, the Netaheat (possibly the one
you had) was not very different.
About the only thing that's different with the modern boilers is that the
ignition is no longer in two stages, because the gas rate is variable.

Yeah, at the end of the day, the start up sequence is fairly standard,
other than that the rest is just refinements


--
geoff