Central heating issue

[raceboy]

Currently having an issue with a few radiators not getting hot, they have all been bled and there's not a drop of air in any of them, the valves would also imply the rads are 'on'.
Other radiators in the house are piping hot, it's just one in the en-suite, and two in the kitchen, one of those gets luke warm, the other stone cold all day every day.
My knowledge of these things starts and stops at bleeding them, so what do I try next before looking like an idiot to a plumber because it's something blindingly simple.

[Saleen836]

Do the cold radiators have adjustable valves? If so unscrew them and with a set of pliers gently pull up the pin....
https://www.youtube.com/watch?v=phFW-IIsH54

[raceboy]

The cold kitchen rad does have a decidedly dodgy looking TRV on it, just been reading something else that suggests tapping the central pin to see if it's stuck, that's going to be tonight's first job.

[Sheepshanks]

If it's not that then it might be balancing - do they get hot if all the other rads are shut off?

Is the system open-vented (with a small header tank in the loft) or sealed (with a pressure gauge somewhere?

[fastbikes76]

Saleen836 said:

Do the cold radiators have adjustable valves? If so unscrew them and with a set of pliers gently pull up the pin....
https://www.youtube.com/watch?v=phFW-IIsH54

just make sure you do not pull it too far...there is NOTHING stopping it coming full out and ending up a hell of a mess. Ask me how easy it is to get back in when you have water spraying you in the face

Normal trick is to spray the pin with WD40 and then a few gentle taps with the back of a screw driver should get them spring loaded again.

[raceboy]

Sheepshanks said:

If it's not that then it might be balancing - do they get hot if all the other rads are shut off?

No, tried that.

Sheepshanks said:

Is the system open-vented (with a small header tank in the loft) or sealed (with a pressure gauge somewhere?

Don’t think there’s anything in the loft, it’s a Combi boiler.

[fastbikes76]

raceboy said:

Don’t think there’s anything in the loft, it’s a Combi boiler.

Then it will be sealed system, somewhere there will be a pressure gauge and a filling loop to top the system back up. If you have been bleeding rads and not topping the system back up, that will most likely be the issue.

[Sheepshanks]

raceboy said:

Don’t think there’s anything in the loft, it’s a Combi boiler.

It'll be sealed then.

Have the rads ever worked? We've had a couple of Drayton (ie pretty expensive) TRVs fail and they keep the rad off. The cheapy ones have all been fine. Just taking the head off (unscrew the collar) might bring the radiator on, without having to meddle with the pin.

[raceboy]

Sheepshanks said:

Have the rads ever worked?

Not sure to be honest, I don’t think so.
Took the TRV off and the plunger could be pushed down, so don’t think it’s that, the pipe from wall to TRV is stone cold, I don’t think it’s plumbed in!

[Sheepshanks]

Check the valve at the other end (probably a 'lockshield' valve under a plain cover) and make sure that's open.

It's a bit of a faff on a sealed system, but (with the system off) shut the trv and bleed the radiator, then shut the valve at the other end and open the TRV and bleed again. Bleed a decent amount of water out - my FIL used to fit CH and he'd bleed half a bucket out to make sure there wasn't air trapped in the pipework.

You'll have to keep adding water to re-pressurise the system. The other issue is you'll dilute any inhibitor there is in the system, so it'll need replacing.

If they've never worked are they all near each other? Could be a pipe has been crushed etc. Mate had a new house where some rads didn't work and they found a wodge of wire-wool in one of the pipes.