Worcester 24CDiOF burner lockout

[Jestershead]

Hi all,
I'm getting a reasonably intermittent burner lockout on the boiler (meaning every third or 4th ignition fails). I can see a strong spark across the electrodes, which are in good condition and position.
Following the fault diagnosis, the resistance across the brown and violet wires to the gas valve are both less than 100ohms (67 and 65), which leads to the diagnosis that the control board needs replacing. My question is that if it was the control board would it not be a constant fault, and not intermittent?
I just wanted a second opinion before I splash out on an expensive part.

Thanks.
JH

 

[keego]

Could be the flame rectification sensor, try that before you go replacing PCB's

 

[Jestershead]

Sorry, I missed out part of the fault description.
It only fails when trying to ignite with a demand for either DHW or CH.
If it manages ignition, it appears to run normally for the duration of the demand, and never locks out after its been running.
More that I should have included at the start: The system has not be altered in any way for several years, its about 6 years old, and holds pressure at 1, which rises to about 1.2 when running.

Would the flame rectification sensor still be a suspect?

Thanks for the reply.

 

[gas4you]

It only fails when trying to ignite with a demand for either DHW or CH.

What else would it be trying to ignite for

Check the gas valve is not sticking and not opening every time it tries to fire.

 

[Jestershead]

I meant it fails for both, not one or other. I guess thats a daft thing to say in professional eyes, but I thought it worth mentioning!

Is there any visual, or other way of checking the gas valve without removing it? I don't know that much about boilers (obviously), but I know to leave gas stuff alone.

 

[gas_man_gaz]

the old gas valves on the cdi are common for stickin (norm happens on 1st demand and then can be ok)

when ya say it fails on ignition does the burner ignite? and does it carry on sparkin?

 

[Jestershead]

If it fails, it sparks repeatedly for several seconds, but no flame appears. I can't tell if theres any gas coming out of the burner, but I presume there isn't. The electrodes for the igniter are in good condition, and well positioned, so if gas was escaping, I would expect it to ignite.
If I press the reset, it usually ignites straight away, second spark.

Is the gas valve a servicable part (not by me), or would it be a replacement?

Thanks.

 

[nickso]

classic sticky gas valve symptoms for this boiler.

almost guaranteed to be the GV. its not a serviceable component by anyone so you will need a corgi to replace it.

 

[pannierstan]

Make sure ignition pressure is correct or slightly higher than it should be.

Stan

 

[nickso]

Make sure ignition pressure is correct or slightly higher than it should be.

Stan

er yeh ...gas valve after what stan said

 

[Jestershead]

Thanks Guys,
I was leaning towards it being the gas valve. (I am an engineer, but different field of experience)

I'll look up someone to come and have a look at it.

Cheers all.

JH