Noisy radiators on unvented system

purpleparrotuk

Had my central heating upgraded a year ago. Most of the radiators were changed along with a new system boiler and unvented cylinder etc. When it was finished I asked a few questions on here and the internet because the engineer didn’t leave me with a bypass radiator and I have no bypass valve fitted. The boiler has a built in bypass. So I got him to come out a couple of months back and he has now made the hall the bypass. I have an evohome system fitted with trvs on all rads apart from the hall and a normal one on the towel radiator.

So the problem I am having is when all the rads shut down the hall radiator hisses like crazy and also some other rads around the house but the hall is the worst. I have read this happens because the boiler is trying to cool itself down before shutting off. Should this happen all the time? I am concerned my system is not functioning correctly and I’m sure this bad hissing should not be happening. I have the flow on 65 and the pressure is fine at the boiler. Can someone please help?

southcoastrgi

A bypass rad should have two lock shield valves on it ie not ones you can easily shut off, the boiler may not require a bypass if it has one built in but if it does still require one then it normally states how far away it should be & this distance isn't normally practical so this is why a rad is used.

Open up both of the hall rad valves fully

purpleparrotuk

southcoastrgi wrote: »

A bypass rad should have two lock shield valves on it ie not ones you can easily shut off, the boiler may not require a bypass if it has one built in but if it does still require one then it normally states how far away it should be & this distance isn't normally practical so this is why a rad is used.

Open up both of the hall rad valves fully

Thanks for the reply. Is it ok to fully open both sides? I would have thought the system would need rebalancing if I do this? There is a lockshield on the left and a pin on the right where the evohome trv was removed. The one with the pin is fully open and the other one is half open at the moment.

fezster

Opening up the hallway rad valve more will help, as the pump is trying to push against a restricted system with all of the other evohome valves closed. But this may upset the balancing and reduce flow to your other radiators.

An external auto bypass valve should be fitted if the boiler internal one is not sufficient. Might be worth checking if the internal one is adjustable?

Also, some TRVs can be notoriously noisy and also particular about being fitted on the flow or return. What make are the TRVs?

purpleparrotuk

fezster wrote: »

Opening up the hallway rad valve more will help, as the pump is trying to push against a restricted system with all of the other evohome valves closed. But this may upset the balancing and reduce flow to your other radiators.

An external auto bypass valve should be fitted if the boiler internal one is not sufficient. Might be worth checking if the internal one is adjustable?

Also, some TRVs can be notoriously noisy and also particular about being fitted on the flow or return. What make are the TRVs?

Hi. Thanks for the reply. They are Honeywell evohome trvs. They are part of the evohome system. I have them on all but 2 radiators. The hall one which is now the bypass and the towel rad in the ensuite. The towel radiator has a normal trv fitted so I can adjust the temperature. It is on all the time is the heating or hot water is on. It used to act as the bypass before the trv was added. Regarding the flow or return question some of the trvs are on the left side but most are on the right. Not sure if this makes a difference.