Pipes making noise even when central heating is off

[TimJoe]

We have a Grant condensing oil fired boiler in good condition and four years old.

Sometimes after a period of use when the central heating has been on, we can hear a rhythmic sound from the pipes and the boiler is not firing up as it should Leave it for a while and turn up thermostat and it works ok without that 'rolling' sound from main water pipes feeding house from the external boiler.

Cannot find a solution to this.

A recent development is after the heating has been on and the thermostat clicks off once room is up to temp, the main pipes feeding from the boiler into the house - behind a wall - are making rushing sounds, or the like a jet engine - that sort of whooshing sound as if water is moving in the pipes, perhaps it's air. This is familiar when the boiler is fired and heating on, but I cannot understand why it's making this noise when the boiler is not firing. The only way I can stop this noise is by powering off the boiler at the mains and the sound from the pipes behind the wall goes instantly.

The noise itself is not bothering me - it's more that I am worried it's indicative of a serious fault. Any advice gratefully received.

 

[exedon2]

What model Grant boiler? Combi? System? Heat only?

 

[TimJoe]

What model Grant boiler? Combi? System? Heat only?

Thanks. It's a 2017 Grant oil condensing boiler - external. I believe it's the Vortex ECO range - heating and hot water. The noise is occasional and is in the piping inside the house before it gets fed to the radiators. When I turn off the boiler at the mains, the sound immediately stops - it's in the pipes not the boiler and sounds like the low jet engine noise we all know when using a hot water tap if that makes sense.