Vibrating TRVs

[beano1939]

I would welcome any suggestions for the following problem.
I have recently replaced some radiators and fitted Drayton TRV4 valves. All ground floor rads are on inverted loops i.e.the pipes run around at 1st. floor level and drop down to each downstairs rad. The system is 10mm microbore. On three of the downstairs rads,the TRVs vibrate when the temperature reaches shut off point. They do not vibrate when fully open.
It is definately the TRV,because a small turn of the knob stops the noise. The jumper must be trying to close, but is receiving back pressure to prevent it doing so. The valves, which are supposed to be bi-directional,are on the return side.
I have tried everything I have read on this site. e.g. bleeding the system with the pump off; shutting down the lockshields to just half a turn open; reducing pump speed to its lowest setting. The rads still warm up, but the valves vibrate, sending shock waves into the system.
It is an open -vented system with 13 rads.The problem is only on 3 downstairs rads. Any thoughts from the experts,please.

 

[Andygasman2010]

This is really odd seeing as the valves are supposed to be bi-directional. I can't think of anything other than faulty valve.

Maybe you could call the manufacturer?

 

[rojaca]

Number of issues really. I believe drayton sya the TRV'S are nominally Bi directional. That is to say, if they make a noise they should be mounted in the correct orientation.
Do you have full interlock on your boiler controls, or are you simply using TRV's to regulate the heat in the property.
Finally does your system have or require a bypass?
The last two points relate to the quantity of water that may be being pushed through a decreasing number of valves as the radiator valves shut off

 

[beano1939]

Thanks for your prompt responses.It seems unlikely that all 3 TRVs could be faulty,so I concluded it must be the system. However it is not a new system[over 20 years old]. It had Honeywell TRVs on all rads and all worked well before. I have gradually replaced rads and fitted new more attractive chrome TRVs over the last 3/4 years. It is only now that the latest 3 are playing up. Although the system can be programmed for H/W
as well as C/H through its motorised valve [Y-plan],we normally keep it on C/H only because we have a Rayburn and a solar system for H/W with their own coils in the tank.
There is no room stat, so apart from the boiler stat,the TRVs control the house temperature. The boiler is an oil PJ Worcester Danesmoor which has full auto control and requires no bypass or heat leak radiator
Thank you, rojaca for your advice about maintaining the flow. I have now tried the system with most TRVs wide open except the 3 suspect ones . It seems to be a lot better although not perfect. So even if the boiler does'nt need the protection of a bypass, perhaps the system would benefit from one. If you agree, then I suppose I will have to wait for a warm day and drain the system down [again] to fit one!

 

[rojaca]

On a 3 port system the dhw circuit will usually act as the bypass. However It sounds like you may have an unvented hot water cylinder withthe twin coil for the Solar? If this is the case you should also have a 2 port zone valve to act as a positive shut off valve on the dhw circuit. If this is the case an automatic bypass should be fitted.
Use of trvs as your principle thermostatic control no longer meets regulation requirements and is not a particularly efficient method of controlling your heating.

 

[D_Hailsham]

There is no room stat, so apart from the boiler stat,the TRVs control the house temperature.

That is not an efficient way of controlling the boiler as it will continue to run after the rooms have reached temperature. It also does not comply with current regulations.

I have now tried the system with most TRVs wide open except the 3 suspect ones . It seems to be a lot better although not perfect.

That means the system is not correctly balanced. Read How to balance a CH system

So even if the boiler does'nt need the protection of a bypass, perhaps the system would benefit from one.

An auto bypass serves two purposes: to maintain the flow rate through the boiler; or, to limit the increase in circuit pressure when TRVs close down. You are suffering from the second problem. Correct balancing will help, but an ABV is advisable.

 

[beano1939]

Thanks for the very helpful answers.
The HW tank is vented [tee off HW outlet on top]. It has 3 separate coils inside : HW from boiler; HW from Rayburn; HW from solar -not much room for the secondary water! There is only a 3-port valve on the boiler circuit:the others are entirely separate systems. Because we have 3 other sources of hot water, 4 if you include the electric heater, then we usually keep the programmer ST699, on CH only. Wouldn't the 3-way valve be closed on the HW side and so not available as a bypass for the CH?
Is it sufficient to install an ABV on the heating circuit after the 3-way valve or should I fit two 2-port valves [S-plan] as well as a ABV and dispense with the 3-way altogether?
Your advice regarding balancing the system is appropriate because I have changed a number of rads and not rebalanced. I guess this, together with an ABV should solve the vibrating TRV problem. I will let you know in due course.
As regards the inadequacy of TRVs alone to control the heating; my system was built without a room stat and so has no wiring for one.Would it meet the regs if I removed the TRV from the Hall rad, which heats the stairs and landing above as well and fitted a wireless room stat e.g. Honeywell DT92E? At least then the boiler would receive more direct switching and not have to rely on it's internal stat to shut down.
Finally and since I am in contact with experts: As I have changed rads and removed most of the crud from the system, would it be a good idea to take the opportunity to fit a 'Magnaclean' filter near the boiler when I drain down?
Thanks in advance for your continued indulgence.

 

[darren17]

whatever room you have the wall stat in there should not be a trv fitted
the magna clean twin-tech or the fernox tf1 twin-tech they are both very good and do exactly the same job but the tf1 is much cheaper

 

[rojaca]

the three port will always give an open circuit-when denergised it is open to DHW.
With regard the wireless stat you should find thisis a muchmore efficient method of controlling your heating and will meet CHeSS standards (essentially those underpinning PART L).
Removing TRV head will give you an open route should TRV'S shut down when valve in CH only though a ABPV is preferable as reduces unnecessary losses through fixed bypass.
Look up the very informative section on system balancing in the FAQ's section for a much more informed breakdown of the subject than I can give.
All the best.

 

[rojaca]

Oops sorry Dave, didn't see your post.

 

[beano1939]

Thanks everyone for your help on this matter. As my initial enquiry raised other points regarding the efficacy of my heating system, I have moved to another thread.