Sewage smell with oil fired boiler, can anyone advise?

Elle · Jan 1, 2016

I have a nine year old condensing oil fired boiler which over the last year has started to smell horribly. The smell is like sewage, and for months tried to track down a sewage problem. But the smell only happens when the boiler is working. I've had heating engineers in three times, and each time they service the boiler, replace the jet, check the flue readings and tell me all is well. The day after, it smells again.

It is room sealed, ie, the flue has both the exhaust and the inlet, and the smell is not of clean burned exhaust gas, so if it is burning OK, as I'm told it is, I can only guess the leakage is of gas when it fires up or switches off. But how could this leak into the room?

Does anyone have any ideas, please?

SimonG · Jan 1, 2016

Condense trap and pipework needs checking.

Geyser · Jan 1, 2016

Any signs of mice in around the insulation?

Best · Jan 1, 2016

Dead mice can smell like really bad sewage odour. Mice love warm spots and below boilers & inside boiler insulation is their favourite places. Have you any signs of mice about?
Your condense pipework might be linked to the sewer and pipework beyond condense trap could have a bad joint.

Elle · Jan 1, 2016

It's not gently toasted mouse, the smell has gone on too long and is different from decaying flesh.
I've just been to examine the condensate pipework, and found there is none, just a drain point on the flue low point!
There is dampness around the pressure relief trap.
The smell happens most early morning, so I'll start to check to see if it coincides with water dripping from the flue or escaping from the relief valve.

Best · Jan 1, 2016

If it is definitely a condensing boiler you have, then there has to be a condense pipe somewhere from it and a trap. Should normally be a white plastic trap (similar to a sink trap) possibly inside the boiler casing and normally a white 3/4" plastic pipe going to another waste/sewer outlet perhaps