What is this noise in the wall ?

[saadandsadder]

I can hear a wooshing noise in the wall.
I can only describe it's as a plane taking off or a fan.
It started when the heating was on over 20 degrees it would randomly start -if I turned heating off it stopped.
Now it's starting when heating isn't on
I turn heating on then off and within 5 mins it stops.
My boiler is show e133
I reset it -it comes on but by morning it's off again flashing e133

I had a gas engineer out who said the noise in wall can't be connected to boiler and no idea what it was.
He didn't know why the e133 was happening
He changed something and the very next day it had gone to e133

The noise in the wall just started 10 mins ago
I turned the thermostat on and straight off and it stopped
The gas engineer said it's not possible.

Any help would be great

Call a plumber instead of a gas engineer.

Next door has tapped into your gas/electric/water supply and your thermostat now controls their cannabis farm heaters and fans?

Sorry, it's Saturday and I'm bored. Nothing helpful to advise apart from get another gas engineer in to sort out the error message on your boiler - a quick google of e133 error says it's a problem with the gas supply to the boiler.

I suppose you have look at what Is near the wall. Is there a chance that there are gas or water pipes in it?

Is there any chance there is a water or gas leak?

Sometimes there is a kind of "blow off" valve attached to the central heating water pipework in case of high pressure etc. We never used to have one in our system, but when we had a new combi boiler installed to replace the old cistern based system, the heating engineer who fitted it insisted on this value being fitted - our is in our garage loft (integral garage) as our boiler is in the garage. Is it possible that it's in your loft and just sounds as if it's in the wall, but is in fact in the loft space directly above??