Knocking heating pipes

[Alexalee]

Anyone have any ideas/solutions?
Lived in my house for 30 years, same heating system, the one with a hot water cylinder.
Last few days when the heating comes on the pipes knock and bang quite frequently for a good hour, same for the hour after it goes off. It's never done this before. Maybe there was the odd single knock every now and then, but this goes on for ages.
Anyone had this before?

We used to have when fist got our house and fitted a new boilers. The pipes were in the floor and uninsulated. As they expanded the rubbed and knocked against each other.

The choice is putting pipe lagging around them if there is space..but some of ours didn't have space so DH put some spacers in between the pipes to keep them apart.

But why has yours just started? Has the boiler been turned up so getting hotter?

could you try bleeding the radiators?

Thanks guys
Dh bled system yesterday but no air in any rads.
Nothing has been changed on the boiler at all... that's the bizarre thing

I hear this from upstairs neighbour's flat. It sounds very similar.

It's not been resolved, but doesn't happen if the radiator thermostat is set low or high. It's in a room that isn't used much and has another radiator anyway, so I think she keeps the noisy one off or very low.

is it cetain radiators doing it? Have they got TRVs?

how old is your boiler? has it got a temperature gauge?

It sounds more like it's under the floors in 2 upstairs bedrooms which are directly above the boiler
Yes all rads have trvs
Boiler is 30 years old
Thanks

When we got a new boiler we had the whole system flushed out. I don't know if it was that or the boiler but it resolved it for us.

Stand next to the boiler and decide if it is the boiler or under the floor.

An old boiler may bang as it heats up, due to localised steam in limescale deposits. This will happen as the boiler approaches its highest temperature, and if you turn the thermostat down so the flame goes out, it will die away within a few seconds.

If if is radiator pipes, it will happen as they warm up, and again as they cool down after you have turned the heating off. If you turn off all the upstairs radiators, it may not happen, then will start as soon as you turn the radiators on.

If it has recently started, it might be that your boiler is getting excessively hot due to a thermostat problem. In this case, you may find that the radiator pipes on the flow side feel scorchingly hot.

Thanks piglet
It's definitely pipes
Which side is the flow? Trv side or the other side.
Do you think fernox f4 is worth a try?

the hotter side

if it's pipe expansion due to heat, exposing the pipes and putting felt on the rubbing surfaces will help.

But if heat is excessive, it'll be the boiler stat.

Presumably nobody has altered the floors or done structural changes such as wall removal.

There might possibly be a problem with reduced flow that a cleaning chemical would help, but this would usually cause rads to be cool at the bottom and hot at the top, so not an obvious cause.

F4 is a leak sealer so not appropriate (and to be avoided).

Sorry f3?
I did have a new solid floor laid about 15 months ago but it wasnt like this last winter

Your pipes have probably come unclipped under the floorboards.