Bungalow with single upstairs radiator piping question

alexuk86 · 16 Nov 2025

We have recently had a combi boiler fitted, replacing an old tank in loft system.

We have a loft conversion which has one radiator. I noticed today that when the heating is on, it warms up fine, but makes quite a lot of noise. It sounds like water rushing and under pressure.

I have posted a picture below, but just incase you can't see it clearly - I had a look at the piping below it, and it has one going into the thermostatic valve, one coming out the lock shield. The hot water side with the TRV has a loop just below the valve which also has an isolating valve on it, that goes into the return coming from the lock shield.

The noise seems to be coming from around there more than anything.

My question is - Is that ok like that? Or would I be better off just removing that loop altogether?

cross thread · 17 Nov 2025

It could be removed ,your boiler may require a bypass but a auto one fitted correctly would be needed

Madrab · 17 Nov 2025

As suggested, that's some kind of bypass that's really been bodged onto that pipework.

If it's a new install I'd be getting the installers back and asking them to sort it, shouldn't have been left like that.

alexuk86 · 17 Nov 2025

Madrab said:
As suggested, that's some kind of bypass that's really been bodged onto that pipework.

If it's a new install I'd be getting the installers back and asking them to sort it, shouldn't have been left like that.

It's not a new install as far as radiators, it was just a replacement of the old boiler.

The boiler is a Worcester Bosch Greenstar 4000. Where in the system would I add the correct bypass valve?

Also, is it causing any potential issues being like this?

Madrab · 17 Nov 2025

Shouldn't matter, when replacing a boiler the system has to be taken into consideration and that includes the radiators, as it's all part of the same thing and any work to ensure the system is correct should be factored in. That would include installing an Autobypass if the system needs it.

alexuk86 · 17 Nov 2025

Madrab said:
Shouldn't matter, when replacing a boiler the system has to be taken into consideration and that includes the radiators, as it's all part of the same thing and any work to ensure the system is correct should be factored in. That would include installing an Autobypass if the system needs it.

Ok. Boxt installed it so I'll get onto them and see if they will do something about it.

Im not a plumber by any means but I can solder pipe and do the replacement if need be. Just don't know where it should be if I end up having to do it myself.

Madrab · 17 Nov 2025

The system needs to looked at and then it needs to be understood if it actually needs a bypass, the installer should have made that determination when installing the boiler - if needed the 4000 would need a bypass circulation loop of ~ 3m, so needs to be installed in a suitable location.

An autobypass is usually compression so no soldering normally needed and where that current ISO is located may be a suitable spot but it also needs to be set up correctly for the specific system requirement.

alexuk86 · 17 Nov 2025

Madrab said:
The system needs to looked at and then it needs to be understood if it actually needs a bypass, the installer should have made that determination when installing the boiler - if needed the 4000 would need a bypass circulation loop of ~ 3m, so needs to be installed in a suitable location.

An autobypass is usually compression so no soldering normally needed and where that current ISO is located may be a suitable spot but it also needs to be set up correctly for the specific system requirement.

Thanks for your help. I'll see what Boxt say!

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Bungalow with single upstairs radiator piping question

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