Heating return issue

2 May 2008
Reaction score
United Kingdom
Hi all,

I have a unvented central heating system running off a 25kw biomass boiler. I have an issue with three radiators in the house not heating correctly. The flow is hot but the return is warm.

The three new rads are on 15mm pipe with reducing down to 10mm on the drop to downstairs. It then comes back up in 10 and picks up the 15mm return.

I have just pulled some floor boards out and discovered that the 15mm return has then been connected up to 10mm tails left by the removal of an old rad.

Could this be the problem? Thanks ALex.
Sponsored Links
If so, would the solution be to replace the old 10mm tails with 15mm back to the main 22mm circuit? Thanks once again.
Yes, I should have mentioned that I have already done that. The rest of the house is piping hot with most rads only on a half turn.
Sponsored Links
I have a 22mm ring with 10mm drops for the rads. He has taken one of these drops and fed another 15mm ring feeding 3 rads in essence. It's difficult to explain..... Sorry!
Does this drawing make it a little clearer.....


  • image.jpeg
    65.4 KB · Views: 132
Thought so. Thanks for your help. I think it was done by the last plumber just for ease......
Hi all, just to close this thread. I have had the 10mm removed and replaced with 22mm. Now all works great.

Thanks for all the advice.

Warmest Regards. Alex. (pun intended)

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links