Hammering from pipes

[bobby_la_mesma]

Dear All

I have a worcester bosh 30CDI conventional boiler fitted into an open vented system. I have a "S" plan design. I have TRV's fitted to all radiators and and honeywell automatic DU 145 bypass set to 5. I am confident that the system is clear from blockages as most of the piping is new. There are only two old radiators downstairs which I have yet to change.
My Grundfos pump is set to 2.

This has happened twice that I know of in two years, but both were within the past two weeks

The heating has been on for a couple of hours. The system is quiet. Suddenly it sound like a motorbike is being driven through the house from vibrations through the piping. The boiler and pump are quiet. The vibrations seem to be coming from under the flooring and up through the towel rail radiator. If I adjust the TVR on the towel rail from MAX to 3 to noise ceases. If I adjust it back to max it starts again. Its like a hammer drill. I cannot figure out what is causing the vibrations. After 5 mins with the towel rail at 3 the noise will stop and I can put the towel rail back to MAX


Any ideas are greatly welcomed

Thank

 

[Steve69the69Gas]

My guess is the TRV valve is jumping.
TRV could be on wrong side or just jumping = replace it.
But before that take TRV head off - knirled ring & check the pin under to see if it moves - push it down & see if it rises up again or not.

 

[bobby_la_mesma]

I just checked the pin and it does move in and out freely. Thanks for the tip. I shall change the TVR ASAP.

Rob