Central heating not getting to all rads after attic conversion

I have an oil fired central heating system.

I did an attic conversion in October/November, 2024 which added to two largish bedrooms, bathroom, and landing to upstairs. While the radiators upstairs are fine and work well, I've noticed that some of the downstairs radiators are not working. Just wondering what to do now, is there a way I can get increased capacity from my existing system? Thanks

Hello,

Have you tried rebalancing the rads?

If so, my next move would be to get the system flushed. It'll cost you €450 upwards, but really should be done every 7-10 years, regardless of the recent changes made.

Turn off all upstairs radiators.
Do the downstairs ones now heat up fully ?

If yes, you probably need to balance your system. The flow to the upstairs radiators needs to be restricted. This is done by closing down the lockshield valves until all radiators heat evenly.

If no, there might be airlocks or air in the downstairs radiators.
Turn off all radiators. Set your circulation pump to full speed.
Fully open one radiator and run the pump for a few minutes. Turn off the pump. Turn off the radiator.
Repeat this for all the downstairs radiators.
When all radiators are done turn on all the radiators and bleed each one.

If it is oil heating you probably need to bleed the under performing radiators. Buy a “bleeding” key for about €2.00 and bleed radiators until water starts to exit.

If yours is gas heating don’t do the foregoing and have a look on YouTube re bleeding radiators powered by gas.

While not the cause of this particular problem bear in mind that your heating loop is now probably a closed loop post the attic conversion rather than an open loop meaning you'll need to top it up occassionally (possibly every 3-4 months). There should be a mains water valve in the attic eaves for the purpose of short top up.

Make sure the valve pins aren't sticking!

@jdwex Thanks so much for this ! This just fixed a small radiator of mine that has been out of action for a while !

Leper said:

If yours is gas heating don’t do the foregoing and have a look on YouTube re bleeding radiators powered by gas.

Click to expand...

It's the same process for gas fired, the variation in methods will be down to whether your system is pressurised where you'll have a filling loop or a vented system where there will be an expansion tank, usually in the attic. Gas and oil systems can use either method.

You’re wrong Leo. We upgraded to gas heating some years ago and the whole process of bleeding radiators is much different. Ask any plumber.

Leper said:

You’re wrong Leo. We upgraded to gas heating some years ago and the whole process of bleeding radiators is much different. Ask any plumber.

Click to expand...

I don't need to, I've had gas systems that were pressurised and unpressurised. I've bled, drained, and refilled both types. My current oil fired system is pressurised, and so after bleeding rads you have to ensure you refill and pressurise. Some newer boilers have built-in filling connection at the boiler itself, others like mine have it set up by the hot water tank where the filling loop is only connected as an when required (specified as a requirement by some of the manufacturers, but based on UK water regulations).

Why would you think that the fuel itself makes any difference? It's not like the water in the heat exchanger knows!! Have a read of this to learn the differences.