Radiator problems

[HPrior]

3 of our radiators aren't working. All others plus hot water is working fine. Have bled all radiators and re-pressurised boiler. The 3 problem radiators aren't working at all ie the pipe leading to them isn't hot either. We recently had an extension where we moved the boiler, changed the position of a couple of radiators and added underfloor heating to one room. All 3 of the radiators that don't work haven't been moved/changed.

Any ideas welcome please! I'm cold!

Thanks

Just to add all of the the radiators in the house are quite new - all less than 3 years old.

We have a (hidden) automated valve that can shut off all the upstairs heating during the day while the downstairs is still on. Could this be the case - that those ones are on a separate zone and a valve somewhere has failed?

Thanks for your suggestion. There isn't an upstairs/downstairs divide (2 cold upstairs, 2 cold downstairs). I actually just realised it's 4x radiators not working (not 3) - one room has 2 and one of them is cold. Suppose it could be that the ones not working are connected to the same valve...

How recently did you have the plumbing work done? We had this scenario when we changed a radiator for a vertical one, it didn't work for the first 2 days, and two other untouched radiators were also stone cold when the heating was on. Then, they just all started working! Our plumber said it was air travelling round the system?

Interesting - we had it done in August and turned the heating on about 2 weeks ago

Sounds like the system needs to balanced. The hot water is taking the easiest route through the C/H system.
If you have thermostatic valves (TRV's) fitted to rads open them all to max. Also ensure all the isolator valves on the other side of the rads are open.
Start the heating and go round to see which rads are hottest and which are cold. Mark the isolation valves on the hot rads and close in one full turn.
Recheck the cold rads. Repeat sequence until the heat is evenly balanced around the system.

There will be one rad on the system that won't have a TRV. this is the heat sink to remove heat if there is a control failure.

This process can be more accurately done with an infra red thermometer, you might have one for the kids temps if not they can be got from Screwfix or Toolstation.

Once you get full circulation bleed the rads again.

If balancing does not work there is an airlock in the system, drain and refill. Don't forget to add corrosion inhibitor.

Hope you get cosy soon.

First I would turn all the hot ones off and see if the cold ones warm up. You may have an airlock (I have suffered from this in the past - well the heating system not me personally!)

Out of my 52 previous posts on Radiator balancing, this one looks quite comprehensive:

www.mumsnet.com/Talk/property/a2205419-New-radiators-not-getting-hot#50023831