Pump/pipe sometimes bigger noise?

Hi all,

I have unvented cylinder & heat only boiler installed a few months now. Once the boiler is on, I can hear the sound or light noise comes from the cylinder&pump room, it is normal and fine. But recently, a few times now, I can hear that sound&noise becomes bigger after the boiler on about some time, then disappeared, and back to normal noise.

Could it be pump issue or pipes? Is this something to be worried?

I know even if I hire a gas engineer to come to check, probably he wouldn't be able to find the issue, as most of times, the sound/noise from cylinder&pump room is normal---even and light, only I notice the bigger noise a few times recently (Maybe it happened before but I was not aware).

This question maybe difficult to get answers here as it may not be clear or common? But anyone has has kind of experience or knowledge to let me know what it is going on, then I would be lucky to get it here I think!

Might be at the end of the heating eg when the rooms upto temp and the auto bypass is opening etc as the 2 port valves have closed

ShaunCorbs said:

Might be at the end of the heating eg when the rooms upto temp and the auto bypass is opening etc as the 2 port valves have closed

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Thank you Shaun!
Next time, if I hear this bigger noise again, I will go and check the port valves if they are closed.
But as after bigger noise, the noise level is back to normal level, so I doubt the port valves have closed? i.g. once the port valves have closed, the pump will not be operating & boiler will stop working, so no noise? Or noise will still be on?

Depends if you have pump overrun eg to get rid of the excess heat after the boiler has finished

ShaunCorbs said:

Depends if you have pump overrun eg to get rid of the excess heat after the boiler has finished

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Thank you again!