Worcester Heatslave Random lockout

[markadams]

I have a Worcester Heatslave 20/25 with bentone b11c burner, The burner has started randomly locking out, it can run for 30 minutes or 10 hours before locking out, it always resets and fires straight away.

I have cleaned the oil filter and checked the photocell which are all fine.

I do a lot of boiler repairs on gas boilers but not on oil boilers.

Any advice?

 

[markadams]

The CPA readings are:
O2% 7.4
CO2 % 10.0
CO ppm 61
XAIR % 54.8

 

[magicno1]

Coil most likely.
Do your tests if you’re trained shouldn’t be too difficult.

 

[markadams]

Thanks for the reply, I have checked oil pressure and all fine and CPA as above.

I suspected the photocell initially but it seems a bit too intermittent for that, so my thoughts were the control box. Why do you think it is the coil?

 

[magicno1]

Have you got a multimeter?

 

[markadams]

Spot on with your diagnosis, tested it when working it was 2.2 k ohms, then goes to O/C when it fails then fluctuates and comes back to 2.2 after a few seconds.

Yes I have three multimeters and lots of other test equipment as I am an electrician as well as a heating engineer.

Thanks again, I will get one ordered.

 

[magicno1]

pleasure

 

[Best]

Surprised it was the coil as they don't usually fail in long periods of hours, unless that is the burner is firing in short time periods and allowing the coil to cool for a long period, such as if boiler just doing the hot water, or low demand circuit.
Generally coils fail either totally, or can work in near permanent burner running conditions in periods of up to about one hour max.
Usually so little time to lockout that I wait to prove it failing.
Another thing to be aware of the Bentone B11 burners is the motor can give trouble and cause intermittent lockouts.
The 10% Co2 is a bit low for that burner. Should be 11% minimum. All the other readings will then become more normal

 

[magicno1]

Top info

 

[markadams]

Thank you Best, thats useful information. What are the symptoms and how would you test if the motor is failing?

 

[markadams]

I Adjusted the air adjustment and the new readings are:
O2 % 1.2
CO2 % 11.2
CO ppm 62
flue temp 200.5 oC

 

[oilmark]

Oxygen reading correct there?
Probably should read 5.2?