Central heating causes noises in wall

[richie51]

I moved into a bungalow 7 months ago and over the winter I've heard loud popping and cracking sounds which seems to come from the wall in the living room where the fireplace is. It starts about half an hour after I've put the central hearing on. It's not continuous but every half an hour or so I hear a loud crack. The radiator is on the opposite wall though. I did have a plumber doing a job for me a couple of months ago and he did say noise travels along joists so it might not be coming from that wall. He said the heating pipes will be under the floor on the opposite side of the room. I looked under the floor but the pipes are all lagged, nothing that would be banging against joists. I looked under the floor by the fire but I can't see anything amiss there. I'm not sure why there should be noise by the fireplace. The noise seems to move around that wall as well, sometimes further along away from the fire. I looked in the loft where there is a water tank, but everything looks ok. There was one pipe not lagged, so I lagged it but it's made no difference. What could be causing this noise? It's as if something is expanding with the heat and creating noise. It happens an hour or two after the heating goes of as well. Can anyone think what might be happening here? Thank you.

 

[Best]

What sort of heating boiler and system have you, and where is the boiler located?
Sometimes the pipes are run up the side of chimney inside a casing

 

[richie51]

It's a conventional boiler. I had a combi in the last house. This is a Potterton conventional boiler which is in the kitchen. There is a flu for the gas fire. The previous fire was condemned as the flu didn't meet standards so I've had a glass fronted gas fire fitted with the flu fitted to the outside wall. The installer didn't mention anything about pipes inside the chimney though. What do you think? Many thanks.