Bathroom bypass - noisy central heating system when shut

[steve958]

Hi - I'm hoping I'll be able to get some advice ....

We have a vented, gravity fed system with an expansion tank in the loft. There are 15mm pipes upstairs and 8mm downstairs. We've done a lot of work to balance the system to get reasonable heat downstairs.

However, my question is about the 2 bypass radiators in our bathrooms. When hot water is heating these radiators heat up too even when the heating is off. When a plumber came recently to fix a new radiator he noticed the T valve for the bypass in the airing cupboard and turned it right down to restrict the flow to the bathroom rads. He said it would increase flow downstairs to the 8mm. This has increased the heat downstairs and I've noticed the boiler isn't firing so much, which is good. However, it has created some noise issues:

- we now get what seems to be hissing pipes / TRVs on the 15mm pipes and to some extent on the 8mm too;

- the pump (which is set to 3) seems to be more noisy and like it's struggling somehow?

- the boiler is really loud when it first fires up and then seems to reduce output.

I have two radiators open continuously so there is always a flow. Does anyone have any advice on he 'hissing' or the pump noise levels? I'm not that keen to open the bypass much more as it seems a waste of heat?

Grateful for any advice.

thanks!

 

[bhm1712]

pump on 3 is too high. I have the same setup, 15mm up and 8mm down which is rubbish for balancing. There will always be noise associated with this setup (especially with pump on 3) because the LSV on the upstairs rads have to be screwed down alot to get some flow down the 8mm from the 22mm main pipes as opposed to all the flow going through the 15mm pipes. I have my pump on 1 due to this and it works fine. The LSV will probably have to be no more than 1/2 turn open upstairs.

with regards to the bypass - what type of system is it? fully pumped or gravity HW and pumped heating? do you have any zone valves?

No heat should reach the 'bypass' radiators during normal HW operation. Normally the bypass serves to dissipate heat during pump over run, not whilst the HW is heating up.

List more details: what boiler? what type of system? how many radiators on the 15mm and how many on the 8mm? any pictures of the setup?

 

[steve958]

Hi - thanks for your advice. I tried turning down the pump and the 'hissing' sound is a lot better. Unfortunately however the rads downstairs don't heat up very effectively as a result, even when all the rads upstairs are off!

We have 4 rads upstairs (on 15mm with TRVs) plus the 2 bathroom rads (fed from 22mm), and 6 rads downstairs (on 8mm 4 with TRVs). The bathroom rads do when HW is on - I think that's part of the bypass. Ever since I part closed the valve (through a turn handle in the airing cupboard) the pressure noises seem to have started, albeit with much bette rheat downstairs! Sorry I can't get a photo but there is a T value with 3 port setting?

I think it is fully pumped - the pump comes on when just HW is on.

The boiler is a Baxi Solo condensing 30HE.

Any further advice would be much appreciated!

thanks

Steve

 

[bhm1712]

if you have a 'T valve' as you call it, it sounds like a Y plan fully pumped with 3 port mid position valve.

This bypass is setup wrong completely. The bypass rads shouldnt get hot with just HW on. What happens in summer?? if its 25 degrees and you want a bath, do the bypass rads still get hot????

The solo 30HE does not require a bypass, so god knows why its setup that way....the only bypass you might want on there if your using TRV's is an automatic bypass valve - since yours is the same setup as mine (apart from mine is semi gravity and not fully pumped) pipework wise when the TRV's start to close, the increase in system pressure makes more noise and so the Auto bypass helps to reduce this noise. There is no problem with using a bathroom rad as a bypass in this way, but it must not have a TRV fitted.

Id like to see how your pipework is installed to warrant having 2 bathroom rads on a bypass from 22mm pipe, the rest on 15mm and 8mm. The boiler manual states: NOTE: On Solo 30 HE models 28mm pipe should be used to connect to the boiler flow and return.

 

[bhm1712]

your pump setting may need to be on 2 or 3 , as not all houses are the same, i admit that. You need to sort this bypass out though before you will know for sure.