One Radiator isn't very hot

[MarcMCFC1986]

Hello

Before I start, I know next to nothing about plumbing - so any replies would need to be written in very simple terms...any jargon, technical terms, or abbreviations/acronyms are going to confuse me further!

Just moved into a new house, which has a Baxi 105e Combi Boiler. Seems to be working fine, apart from a minor problem.

When the heating comes on, they all heat up quickly and the heat is really pumping out of it - but then, after about 20 minutes one of them isn't hot anymore. It doesn't go cold, it's still warm to touch, but not warm enough to actually make any difference to the temperature of the room. Eventually it will heat up again, but then the temperature drops in a different room.

I've mentioned this to a few people who have all said it is an air lock and to bleed the radiators, but I have done this and no air came out of any of them - just water started coming out as soon as I turn the key. I've also seen on some forums that you shouldn't bleed radiators which have a combi-boiler?

If there is an airlock in the system somewhere, should I find it first time? Or shall I go round and do the bleeding a few times in case the airlock is in a pipe somewhere at the time that I'm trying to do it? Or should I not be bleeding them at all? And when the water comes out how do I top up the water in the system? Is that the same valve as increasing the pressure?

Also, there are only the temperature dials on the front of the boiler - I haven't got a Nest/Hive thermostat attached at the moment. The boiler is in the utility room on the side of my house, not actually in my house.

Any advice is much appreciated!

 

[lemon_1]

Probably sludged up. Turn all other radiators off. Set the temperature high on the boiler. Run it for a while. It should force circulation and any crap in there will dislodge. If you still have a problem take a rubber mallet to the radiator and give it a few whacks whilst running to dislodge the sludge

Do you have a magnetic filter installed?

 

[alan333]

When your problem radiator (rad) goes cold... try turning off the other rads (or some of them at least) thus forcing the water to go to the cold one. If this works then your problem could be balancing...
'Balancing' is adjusting the flow to each rad to compensate for how far away it is from the boiler - the farthest one from the boiler might need more water flow than the nearest one, since it loses heat on the pipework on it's way etc. Or it might be that a certain rad has some awkward corners in the pipework (or some blockage) so the water doesn't flow so well to that one etc.
At one end of your rad you might have Thermostatic Radiator Valves (TRV's) - these usually have numbers on them to control the room temperature. Alternatively you should have bog-standard valves which you turn to open or close. However at the other end of the rad you'll probably have valves with a cover over the top - removing the plastic cover gives you access to an adjustable valve. Screwing this valve (using a pair of suitable pliers) works just like a tap on your sink - clockwise slows/stops the flow, anti-clockwise opens it up. Try slowing the flow to the 'best' rads thus allowing/forcing more flow to the bad one.

 

[MarcMCFC1986]

Thank you for your tips. I'll try both these things.

However, would either the sludge build up or the balancing be viable solutions when you consider that the radiator does get very hot to start with, but then becomes only warm?

Presumably if their was a sludge build up or balancing wasn't right then the radiator wouldn't get hot to start with?

I'm not doubting your knowledge - just reminding you of this part of the problem as it doesn't seem to add up!

 

[alan333]

It could be a faulty TRV (if the bad rad has one), but first thing to do is to turn other rads off to see if the problem rad stays hot with the extra water flowing to it. If it does then this would rule out the TRV and point towards water flow problems. If it doesn't then perhaps the TRV is faulty - the top section of the TRV can be removed to access a small pin (on the valve body) which moves in/out to control the water flow. The pin can jam, and sometimes a few 'movements' of the pin releases it.

 

[D_Hailsham]

If the problem rad has a TRV, remove the head, then check if the problem remains or goes away.