radiator (s) tapping noise i would like to stop

[snapper01]

system: baxi back boiler, old but well serviced and no apparent faults.
all following work done / fitted 12-18 months ago:
replaced all rads along with most of the 15mm pipework. new header tank and immersion / heat transfer tank fitted. system flushed several times and has run for 12 months trouble free.

hot water side of system has run alone throgh summer fine now I have come to use the heating as well.
before running pump for the first time in 6 months I checked all the rads with the system cold - no air to bleed. Ran the pump for 1/2 hour without heat, turned off and tried to bleed again - still no air good.
'extra hour' function used to run heat and hot water together for and hour - no unusual noises and everything did what it should.

crunch time: I set the timer to put heat and hotwater on together in the morning at 5.30. at 5.35 I was awoken by what sounded like a little man tapping a hammer inside the radiator in the bedroom, all the rads were still cold and the noise / problems was only evident in one other rad the boiler / pump were quietly running. I swiftly turned the heaing (pump) off and the noise stopped, the hot water was fine as it usually is.
I have since tried running the system and can replicate this fault only in the morning - bizzare.

the system is clean and functions fine, it just makes a god awful noise.
I doubt its doing any damage and the rads all heatup fine,
I dont think its expansion/movement and it seems to be comming directly from the valve (s).
opening the valves / stats stops the noise but unballances the system
the rads are one up and one down, neither at an extreeme of the system
there is no air in the system

could the pump speed be too fast? never changed it.
why would it affect only 2 rads that were fine last year?
could it be static discharge between valve and rad - ptfe insulation between the 2 ??????



ahhhhhh help

 

[Nige F]

Trv. not bi directional...and fitted on wrong end OK it`s always been that end but..........worth checking which pipes heat first

 

[snapper01]

clarrification:
one rad has TRV on the 'out' end, is single direction and has an arrow on it in the correct dirrection
seccond rad is the downstairs 'bypass' rad so doesnt have trv!

 

[Nige F]

System should be balanced by adjusting the lockshield valves, try this Should be instructions here@ diy.not

 

[snapper01]

thanks for the responses

the system is as balanced today as it was last winter .....

Ive just run the system for another 'extra hour' and there was no noise / air / cold spots, perfect really...

I'll re test it tomorrow morning on timer 'cos i'm guessing it'll do it then, as it did this morning, it seems not to like the morning....

any more ideas? all welcome!!!

if not watch this space ......

 

[Nige F]

Then it`s stone cold from overnight....I am thinking pipe trapped agaist joist etc. most common..and sound travels

 

[stem]

I had same trouble last year after moving some pipework. the noise was just as you describe, woke the whole house.

To test I set the boiler stat to off. The following morning the system came on and just circulated ambient temperature water around the rads and was silent, so I guessed the noise was caused by the pipes expanding with the heat.

To cure, I lagged the pipes with pre-formed foam insulation, where they passed through joists and/or were close to the floorboards and there wasn't enough room, I used the thinner pipe wrap to cover them. System silent ever since.