Ravenheat boiler not lighting - suspect pressure switch

Hi All

Hoping you can offer some advice...

We have a Ravenheat combi boiler - not 100% sure on model, but the manual with it is for 'RSF 84E(T) - RSF 100E(T)' - it was here when we moved in and the guy before us thought it'd been in about a year or so. This would make it about 2 years old but it wouldnt surprise me if it was older.

Problem is as follows:

A couple of weeks ago it stopped igniting. Pump seemed to be working fine, but no ignition or fan. I dusted off the installation\servicing manual and started going through the fault-finding flowchart. There was no voltage at the Fan, so I poked around to see where else there was\wasnt voltage. When I put my multimeter accross the thing top-right with a tube poking out (which I've found out is the air pressure switch), the fan started up (presumably due to me closing the pressure switch?) I put the sealed front cover back on, and it worked perfectly - igniting first time etc for a week or so.

Now... the same thing's happened three times over the last 3 days - the fan wont start and it wouldnt ignite, but when I 'close' the air pressure switch terminals for a second its fine. It'll turn itself on\off perfectly for hours

The plumber I spoke to suggested replacing the PCB - but I'm not convinced that'll help - if I close the air-pressure-switch terminals, it works fine which suggests to me that the PCB is fine and its infact a dodgy pressure sensor?

I'm just about to buy a new air pressure sensor, but thought I'd post on here first and see if that sounds like the right thing to do, or if anyone's got any other suggestions?

Not certain with these, but some boilers have the pcb check the aps contacts before allowing the fan to start, so if the aps is stuck 'on' and therefore unable to act as a safety device as intended it won't let the ignition sequence go any further.

could simply be the venturi is blocked and not letting the aps work properly, or as you say it could be sticky.

nickso said:

could simply be the venturi is blocked and not letting the aps work properly, or as you say it could be sticky.

Click to expand...

is the 'venturi' the tube poking out of the aps?

chrisbyrd said:

nickso said:

could simply be the venturi is blocked and not letting the aps work properly, or as you say it could be sticky.

Click to expand...

is the 'venturi' the tube poking out of the aps?

Click to expand...

sort of , yes.

the venturi is the part of the flue that the tube from the aps leads to.

If the boiler has 3 lights on the front, with a call for heat disconnect the thermistor wire on the right and refit it. Somewhere in the process the boiler should light which will indicate that this CH thermistor is faulty.

If the boiler has only two lights on the front then that won't happen but the CH thermistor is always the first thing you need to eliminate on a Ravenheat when the boiler won't fire or is cycling

Dont waste your money on an air pressure switch theres nothing wrong with it!

[Edited post to suit Mk1 and Mk2 models]