Worcester Highflow 3.5RSF - burner lights on HW, but not CH

[silverman166]

Pilot lights, fan comes on, but burner doesn't switch on when set to CH, but it is OK on HW.

If both CH and HW are on, once HW has reached temperature, the burner goes out, and the pilot and fan come on again, but no burner.

Could there be a fault on the Gas Valve? It has three solenoids - one called Pilot, one called Main, and the other Hi Low, according to the Instruction Manual. Looking at the valve in situ, the Hi Low one seems to be associated with the burner pressure adjusting points (High(pressure) for HW, low(pressure) for CH). The pilot solenoid would seem to be working, and I presume the Main one is too, as the Pilot presumably wouldn't light without it.

I'm ignorant as to how exactly the Gas Valve functions in detail, and wonder just how the desired gas pressure is selected by the system. As the Electrical Functional Flow diagrams in the Instruction Manual show that the High Low solenoid is only live on Hot Water mode, I presume that when the solenoid is not activated, the gas valve would be left in CH mode ie low? This suggests that this part of the valve defaults to a low pressure ie CH, situation, and would therefore be expected to light. So something else is not activating, but what, or am I barking up the wrong tree?

So why won't the burner light on CH?

I would appreciate any informed comments and suggestions on how to solve this problem.

(Thanks for getting this far, and I hope this long post hasn't confused!)

 

[nata]

Hi!

Hope you had solved your problem because I have the same ... Two different guys said two things (maybe valve and solenoid or relay) , one said we need ventilation after 20 years of boiler being in the same house!
Help how to solve this....

Thanks!

 

[silverman166]

Traced to faulty divertor valve - the internal mechanism had come loose somehow, such that the drive gear, activated when CH is selected, was not engaged with the rack which opens the valve, and consequently the valve was always in the default ie HW mode. Corrected quite easily fortunately, once I'd diagnosed it!
Hope you solve your problem as easily (after due head scratching!)

Also, since then, I've had the divertor valve seized in one position - fortunately, I caught it in time, managed to release the electrical activating head to expose the valve spindle which turned out to be stiff - a quick squirt of WD40 came to the rescue, and a few manual wiggles on the spindle released it, and it's been OK since - relatively straightforward, and saved the cost of a replacement and plumber's fitting charges!

Hope this helps you solve your problem.

 

[nata]

Thank you for your quick response... We checked relay and it looks OK. Divertor valve - we tried manually and we can switch it on radiators, so we had some hot water and heating. It looks that is working... Than we checked gas valve and it looked that does not work.. So we ordered new one cheaper than gas man offered. We just need to wait till part arrives and for somebody to put it in.. Hopefully is that - not very cheap part to try
So finger crossed!