Potterton 40E Boiler

[Hilts2]

If my boiler is turned on having been turned off for a while, it fires up happily. After 30-60 secs it switches itself off. The outbound pipes then proceed to make the most horrendous banging noises. The outbound pipe is split in two - one route goes to the attic, and is very hot, the other I presume goes under the floor boards and is cold. The pipes to the attic are the ones making all the noise. Anybody got any ideas?

[LoungeLizard]

What you have described is consistent with having no flow of water in the whole system.

The banging noise could be water boiling in the boiler and flashing off causing a knocking noise.

The pipe leading to the loft that gets hot is likely to be the expansion pipe; if so then it will lead to the Central Heating Header tank.  It is getting hot because it is the only escape route for the expanding heating and boiling water in the boiler.

My guess is that your pump has failed.  Sometimes they fail and still appear to be humming.

What you describe happened to one of my centra heating systems last week.  Fitted a new pump myself (plus renewed pump isolation valves) for less than �50.