Automatic Bypass Valve

Kiran · 16 January 2020 at 4:59PM

I've just fitted Honeywell Evohome system in my house. All works fine however I'm getting a fairly loud rumbling in the pipes/rad from the lounge radiators. I've done a bit of reading up on this and it appears to suggest that I need an automatic bypass valve. My question is, is there a minimum distance from the boiler that you need to be before you join the flow and return loops? I presume that it needs to be before the first radiator but if it's too close to the boiler does it present an issue? I've got a floor standing oil boiler in my utility room and the pipes disappear under the floor within the height of the boiler (approximately 900mm). Also, is there a minimum length the bypass loop needs to be?

Thanks in advance

Kiran · 17 January 2020 at 9:12AM

Shameless bump, there used to be some really good plumbing and heating experts on this forum and I'm hoping one of them can help

jefaz07 · 17 January 2020 at 9:50AM

What type of system do you have?

Kiran · 17 January 2020 at 10:31AM

It's a Worcester Heatslave 26/32 combination oil boiler.

It's feeding 14 rooms including bathroom, airing cupboard, WC etc. All the radiators are under control of TRV's. Of those TRV's 11 are Evohome TRVs, the remaining are standard manual TRV's.

I've created a temporary bypass by fully opening the TRV's on the bathroom, WC and airing cupboard which has certainly improved the issue. When the lounge shuts down now you get a short rumble/vibration which leads me to think I was on the right track with a bypass being required?

Thanks

Kiran · 20 January 2020 at 7:11AM

One final shameless bump and I'll let the thread die. Any advice gratefully received. It's frustrating as it's making what would be an excellent system quite irritating.

FreeBear · 20 January 2020 at 12:46PM

Kiran wrote: »

All the radiators are under control of TRV's.

At least one radiator should not be fitted with a TRV. This will be the radiator in the same space as the thermostat (normally, the hallway). You do have a thermostat don't you ?

Rodders53 · 20 January 2020 at 4:20PM

Bypass loops are only required:
1 If there's a frost protection thermosat... as no 'call for heating' is coming from any other radiators etc.,. and the valves will be closed to any water flow.

2 If there's a need for the boiler to have the pump 'run on' to dissipate heat in the heat exchanger and the other heating controls shut down the pipework (via 2 port valves).

3 If all radiators have TRVs and there is only a CH timeswitch control (but it is usual to use a bathroom radiator/towel rail as the 'bypass' loop in that situation).

Read the boiler installation manual for the makers' advice ref bypass loops.

You appear to have a different issue along the lines of a water hammer effect when the (motorised) Honeywell TRV on the lounge closes.

It's not unknown for TRVs to make noises when they open/close due to the water turbulance created. Try altering the flow rate via the lockshield valve on that radiator?
Some older TRVs are unidirectional so make sure the flow direction is correct as well?

Kiran · 20 January 2020 at 10:02PM

FreeBear wrote: »

At least one radiator should not be fitted with a TRV. This will be the radiator in the same space as the thermostat (normally, the hallway). You do have a thermostat don't you ?

Thanks, I've double checked and I do have 2 un controlled rads with no TRVs. One bathroom and one airing cupboard. With the evohome you don't have a single thermostat, its built into the TRVs so you can zone your house to different temps

Kiran · 20 January 2020 at 10:07PM

Rodders53 wrote: »

Bypass loops are only required:
1 If there's a frost protection thermosat... as no 'call for heating' is coming from any other radiators etc.,. and the valves will be closed to any water flow.

2 If there's a need for the boiler to have the pump 'run on' to dissipate heat in the heat exchanger and the other heating controls shut down the pipework (via 2 port valves).

3 If all radiators have TRVs and there is only a CH timeswitch control (but it is usual to use a bathroom radiator/towel rail as the 'bypass' loop in that situation).

Read the boiler installation manual for the makers' advice ref bypass loops.

You appear to have a different issue along the lines of a water hammer effect when the (motorised) Honeywell TRV on the lounge closes.

It's not unknown for TRVs to make noises when they open/close due to the water turbulance created. Try altering the flow rate via the lockshield valve on that radiator?
Some older TRVs are unidirectional so make sure the flow direction is correct as well?

Thanks, the trv and lock shield are backwards on a couple of the rads, as I don't know the age of the ones that were there I'll try changing them. The system could probably do with a flush through too. I'll give it a try and see how it goes.

justworriedabit · 11 April 2021 at 11:50AM

Old thread but I hope someone can help.

We've removed one rad to decorate at our leisure. This had a TVR valve. We are waiting for a brand new to arrive, its one of those double designer ones as opposed to the singel we have atm. We were going to remove the top landing one to decorate and its single as well but this one does not have a TVR and we recall a plumber telling us years ago we need one rad without a TVR to "bypass" - So reading up, some threads state we can alos remove the 'bypass rad' and just remove the TVR head/control from another rad this rad will then serve as a 'bypass' - is that correct?
TIA.

Le_Kirk · 11 April 2021 at 1:29PM

If you remove the TRV head, you will be left with, effectively, a radiator that does not have a TRV. It is normally recommended to have the rad without the TRV in the same room as the thermostat to ensure that you don't try to heat the room up to the setting on the thermostat but have the radiator closed off due to the TRV in which case the room would never get hot enough to operate the stat.

Automatic Bypass Valve

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