Noisy/shaky boiler after flue removal

28 Dec 2021
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United Kingdom
Builder temoved the flue today as they had to build the roof of an extension. Extension is still open (no bifold, joists only), but the flue had to go as it was in the way.

Since they removed it, the boiler makes a very loud noise when turned on and it vibrates.

A gas engineer is coming tomorrow morning, but what happened? Trying to understand how a piece of plastic pipe has that effect.

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Turn your gas supply off at the meter immediately and call the emergency service , the number will be on your gas meter, they will report your builder, this is terrible and very dangerous behaviour, blooody builders, think the laws of physics dont apply to them
No, I haven’t been using the boiler, I switched it off almost immediately. I also switched off the gas main, just in case. A gas certified engineer will drop by tomorrow morning to have a look. When I told him what happened, he didn’t seem alarmed.

For the record, there is still a flue in place. It is properly connected to the outside of the house through the wall. Before removal, the flue had a pipe going 90 degrees towards the sky. That bit has been removed, nothing else. The boiler ran for less than a minute, as I was put off by the sound and vibrations.

Anyway, can someone explain what actually happened?

PS: we also have a functional, brand-new co2 monitor above the boiler, I guess it would’ve gone off if the boiler leaked.
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Some photos would help but if the builder has modified the flue system in any way it could negatively affect the way the boiler burns. All modifications to a flue system need to be followed up by flue gas analysis and gas valve adjustments
Right, gas engineer just left. The situation was not dangerous, as the boiler was still working properly and the gasses were evacuated externally. It was just a case of the muffler being taken off, not the actual flue. Everything is back to normal, thanks for your advice!
What is a muffler ? do you mean terminal in which case yes it was dangerous if left in operation with the terminal removed
I have to admit I don't know, this is what I've been told. I'd not expect the engineer to lie to my face, especially since, like I said, all the gasses, good or bad, were still on the outside of the house, in open space. boiler and gas main were switched off anyway, out of precaution.

plastic tube is back and boiler is happy :).
PS: we also have a functional, brand-new co2 monitor above the boiler, I guess it would’ve gone off if the boiler leaked.
A CO2 monitor isn’t what you need and no it wouldn’t have gone off if the boiler leaked products of combustion, you need a CO (Carbon Monoxide) alarm, which usually would sound if the boiler leaked products of combustion.

Also, your builder unless gas safe qualified with the relevant additional appliance qualification shouldn’t be doing anything to your boiler, especially since how you started out the thread, which sounded like he was putting you and others in danger.
OP ... unfortunately you are coming onto a forum that has gas and plumbing professionals giving advice, who have a keen sense of when someone is being given wrong advice.

When your 'gas engineer' mentions that it was just the muffler then that isn't a term that would be used by any normal gas engineer. A muffler is an American term for an exhaust, there wouldn't normally be such a thing as a muffler on a gas boiler flue. That then brings it into the realms of possibility that you are being scammed by someone who is just playing at being a gas engineer or worse, a builder that thinks they know what they are doing when it comes to appliances that can kill.
If the flue was installed and no terminal installed , CO isnt really your biggest problem if it is outside, but depending on the boiler make and model you might get a very big bang without the terminal fitted, but as you say "whatever "
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