Vokera 20/80RS Flowmatic: Burner does not fire up.

[IWB]

Hello, I have had 20 years of no troubles with the no-frills Flowmatic. DHW diaphram and a fan with noisy bearings are the only faults until now.
The burner will not fire up on a call for HW or CH. Both valve switches are actuating and electrically sound. The fan spins up as it should when a call for water or heating is made. The pressure switch for the fan is operating when the fan speeds up. 240v AC is switched to the gas valve solenoid for either service. I am not au fait with what voltages should be seen at the modulator coil but there is a change and that seems to be about 4VDC on what should be the burner start. Pilot is a clean solid flame. There is only one item I cannot test and do not know how it affects the gas valve. That item appears to be a bulb stat with two possibly capillaries (?) running to the gas valve. "High limit stat" (interrupter). It is in a pocket below the safety stat (which shows continuity) and is connected to the rear of the gas valve and also the top right directly under the pilot thermocouple.
Any input to save throwing money in the wrong place would be appreciated.

 

[DP]

Other than saying you have the answer, cannot say anymore. Read your post again. Get an engineer in to fix the problem. Do not let him sell you a new boiler if you are happy with this old work horse. If he says cannot get parts look elsewhere or repost here.

 

[IWB]

Other than saying you have the answer, cannot say anymore. Read your post again. Get an engineer in to fix the problem. Do not let him sell you a new boiler if you are happy with this old work horse. If he says cannot get parts look elsewhere or repost here.

I understand what you mean DP
I do not mind working on the water and electrical control systems but I draw the line at gas components. It put a dampener on my weekend when I realised there would be no Saturday morning rubber ducks in the bath for me.
I will be keeping the boiler for as long as it can be kept safely and reliably functioning, its a workhorse.
Thank you!

 

[IWB]

Job completed by a local old school man. No intake of breath and no trying to sell a new boiler. It took him 5 minutes to check through the gas valve not opening and he suggested it unlikely that the gas valve had failed but likely the high limit stat had stuck in at the rear of the Honeywell valve. I already had the part by then and produced it. He was happy enough because it saved him a return to finish the job. He will come back to service it and check the modulator setting while he is doing that. Happy with the service and thanks for the heads up you diynot folks!

 

[Agile]

There are still some people who can repair boilers without a sharp intake of breath and a quote for a new boiler!

Tony