Boiler Short Cycles only when cover on

[Pedro202]

Good morning everyone,

Have a bit of a unique issue, ive only found 1 reference to it on the internet with no answer. For some quick backstory, in Jan 22 my CH water circulation pump killed itself. This old pump was replaced and i troubleshooted some short cycling and with the help of this forum i got it mostly sorted out.. This was mostly gone butover the course of the last 8 months it has steadily got worse. to the point now where it is a sooted up mess and the boiler cycles constantly off and on.

Doing some troubleshooting yesterday i found that if i run my boiler outside with the front of its weatherproof casing off it fires and runs normally. With the cover replaced it then starts to cycle. What in the world could be causing this? It was serviced late last year so it is due again and i noted this morning that there must be a slight leak between boiler and burner as there is some soot inside. Anyone any thoughts on what this could be?

Thanks in advance.

Pete

 

[oz-plumber]

What Boiler?

3 or 4 reasons why this is happening - quite easy to diagnose depending on type of boiler

 

[Pedro202]

What Boiler?

3 or 4 reasons why this is happening - quite easy to diagnose depending on type of boiler

Thanks for getting back to me Oz.

Its a warmflow Boiler, the plate on the front has 70/90 and 400 scratched on it. no other real markings. With a Riello RDB1 70-90 Oil fired burner. Thats all the markings i can see

Pete

 

[exedon2]

Is it a combi or heat only?
Combustion not correct if its sooting up.

 

[Deleted member 120897]

Usually if it’s working with cover off, then it’s taking in the extra air that it needs for complete combustion. As per @exedon2 - it appears that it’s set incorrectly.

 

[John Coen]

Sounds like fumes escaping inside boiler as it works ok with cover off. Check the gaskets and replace if necessary. There is more resistance sending flue gasses through a condensing boiler.

 

[Pedro202]

So I think I've solved it. Hasn't short cycled so far this day. Removed the photo cell and it was ofcourse filthy. Cleaned it up and reinserted it and the boiler worked much better but still cycled.
Inspecting the photocell it has 2 bumps that stick it the end of it. Almost like losing pins of sorts. The way it was inserted they would have been above and below the sensor. Rotated it 90 degrees so they are now at the side and it has worked flawlessly since.
I will be getting it serviced as there is very obviously a leak from the main gasket but overall its now running perfect and heat is significantly faster than before.