New CH system - knocking rads

[analouise]

Hello experts! I have just had a new CH system installed with Biasi (Riva Compact HE) combi boiler and 4 vertical rads and 1 horizontal. They all have a thermostatic control. The three smaller vertical rads (1800mm tall) are pretty noisy and since they are in the bedrooms this is a problem. Other rads make no noise at all.

They make a loud knocking noise - quiet tapping then gets louder and louder. It happens about every 10mins when the heating is on. Last night it was so disturbing that I turned them off by their individual thermostats and it stopped.

My plumber is being pretty unhelpful. This is partly because he hasn't stuck around long enough to hear the noise and partly because he blames my choice of rads. Manufacturer suggested thermostatic valve might be sticking - told plumber and he says it's not. Or that there might be debris in the system - is this likely with a new system? Plumber has reduced the flow as a result of my complaints but since then the noise has got louder. Have also bled the system so no air left in it. Any ideas????

 

[gasman26]

sounds like the trv`s have been fitted back to front, either swap the offending items end for end or.......
suggest to your plumber that he replaces valves for 4-way reversable flow trv`s (drayton trv 4`s always a favourite)

 

[kevplumb]

stats are on the wrong end of the rads

plumber is a p***k

 

[Sandrounder]

Check to see if the TRV's have a arrow on them, this is the direction the water should flow through them. Turn the heating off long enough for the rads to cool then turn it on and feel which end of the rads get warm first, if the TRV is at the warm end the arrow should point towards the rad, if it is pointing away it's installed backwards. If the other end gets warm first the arrow should point away from the rad, if not again it's wrong. Is it possible the noise is the pipes expanding and rubbing on the floor joist or floor boards? If yes lift the floor board and wrap 2 or 3 inches of foam pipe lagging around them, they will still move but not make any noise.

 

[analouise]

Big thank you to all of you for such speedy replies! I will check the trvs etc... and get back to you. And you're right about the plumber!

 

[Agile]

If there are TRVs on all the rads then the installer should have fitted an automatic bypass ( but might not have done! )

Its only possible to make some guesses about your problem and its really you at home who can best try to see where the noise comes from.

There could be dirt in the system if he did not clean it properly but even if there was it would not be causing the problem.

Part of the problem will be that he has almost certainly not set the boiler heating output to the minimum to match your radiators. That will be the first thing for him to do. It is rather fiddly and few installers seem able to follow the instructions correctly. ( its done from the front panel! )

After setting it as above, the next think to look at is the mounting of the vertical rads. I am guessing that its an expansion/contraction clicking as they warm or cool. Try listening and see exactly where the noise seems to come from.

Tony

 

[kevplumb]

There could be dirt in the system if he did not clean it properly

ohhh what a serrpriiiissse

let's assume you go to a faulty boiler and can't blame the installer OR a dirty system

then your up the creek without the proverbial

 

[gasman26]

If there are TRVs on all the rads then the installer should have fitted an automatic bypass ( but might not have done! )

I do belive the Biasi (Riva Compact HE) combi boiler has an automatic boiler bypass .....

 

[clf-gas]

Automatic bypass integral with Biasi

 

[Agile]

Yes it does, but its only to protect the boiler and an external one is required if there are TRVs on every rad.

Tony

 

[gas4you]

If you have 'straight trv's' fitted to tall rads for looks then not many makes are available that are bi-directional.

Kevs comments about plumber probably spot on but why did you use him in the first place was he cheap If he is this unhelpful over a 'small' problem I don't rate your chances much if you get a serious warranty fault with boiler

 

[gas4you]

Yes it does, but its only to protect the boiler and an external one is required if there are TRVs on every rad.

Tony

Not with new Vaillants

 

[analouise]

Hello again, I got excited then because your theory was right. The TRV's are not on the end that gets hot first and yet the arrows are pointing towards the rad. HOWEVER, they are Drayton trv 4's - does that mean that it doesn't matter which end they are on?

If that's the case then I think the theory that it's under the floor boards might be the right one. Unfortunately, it's not easy to get my floor up!

 

[gas4you]

If you have 'straight trv's' fitted to tall rads for looks then not many makes are available that are bi-directional

Not certain that if they are straight valves that TRV 4's are bi directional. Sounds iffy if ony one arrow on valve body and its pointing against the flow

 

[kevplumb]

Hello again, I got excited then

you get the op exited the floors yours bonny lad