Worcester 35CDI Only Start with Top Cover Removed

[andygiffard]

Hi Guys, Please could you advise? I can only get the burner to light with the top cover removed. In both Heating and Hot water modes. With the cover on I get slow red light flashing. As soon as the cover is removed the system works perfectly . I have cleaned the fan and venturi and all pipes leading to the Air Pressure Switch are fine . The Flue is also clean. All electrical connections are fine. The Fan seems to be running fine and is smooth and quiet. Would I be correct in thinking that the Air Pressure Switch is at fault?
Thanks in advance
Andy

 

[Agile]

You either have to be competent or CORGI to do all that!

Did you wash out the venturi with high pressure water?

If you are competent then you would measure the switch on /off pressure of the air pressure switch.

Tony

 

[kevplumb]

wa wa wa hang on i will get the violin out

yer a friggig spark glazier at best and prob a corgi pa man at worst

dingbat either way

to the OP check the aps is making

 

[andygiffard]

I could measure the switch on /off pressure of the air pressure switch if I had the Spec . I have a Vacuum Tester . I'm an Electronics engineer and also have 30 years experience with Cars and Motorcycles . I dont pretend to be a Corgi Fitter I simply wanted some advise.
Cheers
Anyway

 

[gas4you]

certainly sounds like a classic venturi partial blockage. I always use a compressor to clean them.

Are you sure there are no cracks/splits in the aps pipes? Is the central flue exhaust tube in the flue in place, or has it dropped out at the outside end and laying on the outer flue case?

 

[Agile]

Its often marked on the switch.

They are usually between 0.5 mB and 1.4 mB.

You need to measure the operating pressure of the switch and the pressure presented to it by the venturi.

Strictly you should also test the switch for air leaks as if it was a gas pipe.

There should be at least 0.5 mB margin to ensure reliable operation.

The venturi pressure will vary considerably with the cover off. Many boilers have external pressure test points.

I assume that you have checked the flue is not damaged or obstructed by ivy ???

Tony

 

[clf-gas]

Hi Guys, Please could you advise? I can only get the burner to light with the top cover removed. In both Heating and Hot water modes. With the cover on I get slow red light flashing. As soon as the cover is removed the system works perfectly . I have cleaned the fan and venturi and all pipes leading to the Air Pressure Switch are fine . The Flue is also clean. All electrical connections are fine. The Fan seems to be running fine and is smooth and quiet. Would I be correct in thinking that the Air Pressure Switch is at fault?
Thanks in advance
Andy

If you have cleaned fan and venturi then as has been said, fualty pressure switch, or more likely blocked or disturbed flue.