Bosch combi only works without cover lid on

josep

I need some help figuring this one out.

This combi boiler works perfectly fine like this, with the lid off. Once I put the lid on, it seems like the flame goes off and the igniter fails to light on, so the temperature starts dropping really quick. Maybe air intake gets blocked? Maybe sensors stop working?

If I have the lid on from reset, the boiler lights up once and fails to keep the flame on.

Jamie Hall

Something is blocking the air intake. Something wrong with the way the cover is going on… have to be there to figure it out.

josep

Thanks for the quick reply. Any way I can double check that's the issue?

pedmec

your combustion air is blocked. inspect the combustion air intake piping. is this a new install.

josep

This worked well over 2 winters

Jamie Hall

Wonder what got in there…

Big Ed_4

Birds and critters could nest is the air intake pipe You may need to clear it out… Add a stainless screen insert on the end off of both vents to prevent problem in the future …

Lyle {pheloa} Carter

If you are using a concentric vent on this boiler. It is possible that the exhaust tubing inside the makeup air tubing has become loose or disconnected. This will cause exhaust gases to be drawn in through the makeup air tubing, and the boiler will be unable to fire. When you remove the cover enough fresh air is made available for combustion purposes, however, exhaust gasses will be leaking into the room at the same time. If this boiler vents with any concentric tubing at all, do not run it until the problem is fixed. Twice now I've seen where people have failed to glue the exhaust tubing inside of the wye of a so-called bazooka fitting.

josep

Oh, this one uses the provided splitter. Maybe somehow taking this apart to check?

I also looked at (what I think are) the exhaust and in pipes but didn't see any clear blockages there. No visibles critters or nests

hot_rod

Any way to remove the air intake on top and try it? That would eliminate the intake air piping? Maybe a couple phillips screws on top?

Teemok

If the intake piping is unobstructed, with no bellies/traps and it is not "effectively" too long (flue included), It could be that your heat exchanger is dirty. The unit may have been poorly tuned to start with and has now reached a HX build up level that prevents a good combustible mixture when the intake piping friction is added to the equation. A clear flue and heat exchanger would be my next check and then the state of tune with the door off. A with door on cabinet negative pressure reading might be good to do to verify that the intake is not the problem.

josep

Great insight. It'll be a while until I can do a thorough cleaning like that, but I'll try to report once I do. Thank you!