Ideal Classic pilot problem

[npb]

Hello,
My Ideal Classic FF260 starts up properly from cold and runs for about 3 minutes then shuts down. After another 3 minutes, or so, it tries to start up again with the fan running and the igniter sparking but there's no pilot. The igniter and fan keep going until I switch off at the control panel. When it's cooled down it will start again.
What could be the cause of gas not getting to the pilot when hot?
With thanks in anticipation, Neil.

 

[Dan Robinson]

Could be a jammed gas valve - have you checked for voltage at the coil? It is a job for a CORGI though.

 

[npb]

I'm working from the Installation and Servicing guide that came with the boiler (10 years ago) and yes, in the fault condition, there is 240vac going to the pilot gas solenoid from GV1 on the PCB.
At start-up from cold there is initially 240vac on the common (C, red) and normally closed (NC, violet) terminals of the air pressure switch. The boiler fires and the switch changes over to put 240vac on the normally open (NO, yellow) terminal. Then, for a short time, I can cycle the boiler off and on correctly by adjusting the thermostat knob, down and up.
When the fault appears, there is 240vac on all three terminals (C, NO and NC) of the airpressure switch. How can that be? Is the switch the problem?
Is there a way that I can measure the differential pressure across the switch to see if each is within spec, whatever that is?
Thanks, Neil.

 

[npb]

... and I should have said that the overheat thermostat is not triggered and all the PCB neons stay lit, and the fuse is OK.

 

[Agile]

I suggest you measure the pilot gas valve solenoid resistance both hot and cold.

Or if you have a sensitive clamp on ammeter you could measure the current.

Tony

 

[pannierstan]

Might be a duff PCB. If the relay is dropping out then this will cause a similar fault

Stan

 

[npb]

I'm grateful for your suggestions, and I'll look into those tomorrow.
The Classic seems to be a good old solid long-lived reliable boiler. Has a circiut diagram and technical description been published anywhere?
Thanks, Neil.

 

[Dan Robinson]

Give email address and full make and model number and I sure one of us can send you the manuals.

 

[npb]

Thank you, Dan.
It's an Ideal Classic FF260. I can't find a serial number, unless it's this on the bottom of the spec sticker: MV 111121 9620 03073.
Your help and interst is most gratefully received.
Neil.

 

[npb]

Oops, it's getting late.
You asked for my address.

**********

Thanks, Neil.

 

[Dan Robinson]

I'm sending it to you telepathically....

an email address would be nice - update your profile...



That was a quick edit...

 

[Dan Robinson]

Depending on your serial number I have two manuals...

Are you using LPG? Or is it the slimline model?

 

[npb]

npb Posted: Wed Aug 01, 2007 10:16 pm Post Subject:

--------------------------------------------------------------------------------

I'm working from the Installation and Servicing guide that came with the boiler (10 years ago) and yes, in the fault condition, there is 240vac going to the pilot gas solenoid from GV1 on the PCB.
At start-up from cold there is initially 240vac on the common (C, red) and normally closed (NC, violet) terminals of the air pressure switch. The boiler fires and the switch changes over to put 240vac on the normally open (NO, yellow) terminal. Then, for a short time, I can cycle the boiler off and on correctly by adjusting the thermostat knob, down and up.
When the fault appears, there is 240vac on all three terminals (C, NO and NC) of the airpressure switch. How can that be? Is the switch the problem?
Is there a way that I can measure the differential pressure across the switch to see if each is within spec, whatever that is?
Thanks, Neil.

Thank you to Agile Tony, Pannier Stan and Dan Robinson for you interest and help.

Tony: The pilot solenoid resistance is 5kohms, normally and under fault condition. The main gas valve body does not heat up.

Stan: I've checked all I can on the PCB 25B with an AVO and by watching what happens to the relays and the air pressure switch.

Dan: Thank you for the e-mailed files. I should have made clear that I'm already working to the 40-page Installation and Servicing Manual. I was hoping to find circuit diagrams and details of the PCB and a description of what should happen under what conditions.

From my limited understanding of how this thing works the PCB seems to be doing what it should in response to extenal signals. The air pressure switch is really puzzling - is it not meant to be a change-over action? What makes it switch? How is that all three terminals of the switch show 240vac under fault conditions? What would happen if I removed the pipes from the switch?

At the risk of repeating myself, the fault is the inability to light the pilot after the boiler has been running for a few minutes and when the initial conditions have changed as described yesterday (above).

I'll try anything to figure this out - won't be beaten by simple technology, but I don't like buying parts to swap without knowing which one is at fault.

Anybody got a recommendation on how to proceed?
Thanks, Neil.

 

[npb]

ps The boiler runs on mains gas. npb

 

[ChrisR]

Yes the aps should give nice clean , zeroish and infiniteish readings, but they often fail the way yours seems to have done, and the pcb isn't the only one which is moody about how it reacts!
I daresay you can work out what to do - I'm reluctant to be specific in case you start running the boiler with a defectve fan...