Hammering TRV's

[Ricardus]

The cheap TRVs I brought from Screwfix are driving me mad! I get hammering loud enough I'm surprised the neighbours haven't come around to complain about me using a jackhammer at all hours.

I've bled the air out fully, tried reducing the system pressure down to about 1bar when hot (as well as increasing to 2bar hot) and adjusted the locksheild valves on the knocking rads to reduce flow, but no luck.
The TRVs I have are supposed to flow both ways, and some are on the inlet others on the outlet but theres no commonality between the ones that knock or not.

I've come to the conclusion I need to replace the TRVs with some decent ones (Drayton TRV4's seem popular on here) but should I swap the valves around to they're all on Inlet side, or will replacing with decent TRVs alone cure my problem?

 

[gas4you]

Do they have 1 or 2 arrows on the valve body?

If only 1 then you have cheap valves (typical screwfix cr*p) and they have probably not been fitted properly with the water flow direction.

 

[JohnD]

I presume it is the "piston" that closes the valves, being pushed by the water flowing in a "closing" direction. I suppose it has too much play in it. If these TRVs are on the Inlet side, with the flow trying to push the piston in the "open" direction, I would have thought they wouldn't hammer.

 

[doitall]

The problem is the system and nothing to do with the valves.

Pressure differential is the problem and an auto by-pass valve will cure it.

Next time it does it turn the valve up to a higher setting and it should stop, until that temperature is reached.

Test 2 is remove the head.

Test 3 turn the pump down.

 

[Ricardus]

Do they have 1 or 2 arrows on the valve body?

If only 1 then you have cheap valves (typical screwfix cr*p) and they have probably not been fitted properly with the water flow direction.

2 arrows. In fact I'm pretty sure the plumber who fitted them for me when he replaced my boiler with a combi said "Oh yeah these are rebadged *brandname I cant quite remember, possibly Myson* valves, they'll do."

The ones that hammer the worst are on the flow side, the ones that dont, and will close with an audiable clang if I turn the head fast, are on the return side.

 

[JohnD]

you say you've adjusted the lockshields. these can be turned down a surprisingly long way to reduce flow when balancing, almost to the closed point.

when adjusted, you should (even without pipe thermometers) be able to feel the difference in temperature between the flow and the return pipe with your hand, flow will be "too hot to comfortably hold" and return will be "hot but not too bad." I do it by closing, then gradually opening a fraction of a turn at a time.

There may be a better description. I am just a householder. I presume you have at least one rad with no TRV, in the room where your wall stat is. Do you know where the bypass is?

A photo of your TRVs will help.
//www.diynot.com/forums/viewtopic.php?t=129539

 

[Ricardus]

The problem is the system and nothing to do with the valves.
Pressure differential is the problem and an auto by-pass valve will cure it.

Wouldnt reducing the pressure in the CH have made some difference to this?
I've heard of these. Would I loop one beween the CH flow and return pipes close to the boiler, or one at each of the rads with noisy valves?

Next time it does it turn the valve up to a higher setting and it should stop, until that temperature is reached.

Yep, when it stats knocking again

Test 3 turn the pump down.

I've got a Worcester Bosch 30 combi boiler, I don't think I can without taking the covers off.

 

[Ricardus]

you say you've adjusted the lockshields. these can be turned down a surprisingly long way to reduce flow when balancing, almost to the closed point.

There may be a better description. I am just a householder. I presume you have at least one rad with no TRV, in the room where your wall stat is. Do you know where the bypass is?

I turned them down about halfway closed, might have another go opening them up from fully shut and see what happens. Nothing to lose is there?
I don't have a TRVless rad, though the bathroom rad is set to just under max and might as well be fully open.

A photo of your TRVs will help.
//www.diynot.com/forums/viewtopic.php?t=129539[/QUOTE]
Hmm, Screwfix have changed makes from the cheap TRVs I bought. Perhaps they had complaints?

 

[JohnD]

I don't have a TRVless rad

You should have. Take the top off the one in the room where the wall stat is. Throttle down its lockshield to make that room warm up slowest.

 

[doitall]

Ricardus, it is not the system pressure but the pump pressure (head) that is giving you the problem.

As JohnD said a radiator without a trv would help, but it can make that radiator noisy, an auto by-pass valve fitted in the radiator circuit will cure the problem. preferably away from the boiler.

 

[JohnD]

Point of information (I am just a householder) I've heard that you can't just turn down the pump speed on a combi, like I would on mine. Are there particular rules for how Ricardus should set his pump?

 

[doitall]

The pump is not adjustable, but they do say one radiator should not have TRV fitted