Bleeding radiators (in more ways than one...)

[Peter Kemp]

Folks,

I'd appreciate your thoughts. Long story short:

Just moved into house with an Alpha CD32C boiler in attic and 9 rads. Eight of these work fine.

The ninth radiator stays cold, no matter what setting the TRV's on. The 'needle' in the TRV seems OK (up and down by some millimetres when pressed manually) so I tried bleeding the radiator. A *lot* of air came out. Even better news, without any 'glooping' sounds - as one might expect if sludge were being pushed about - the rad started warming up!

Unfortunately, the bleeding caused the water pressure to drop too low and the boiler shut down. I re-pressurised, started the boiler up again and ...eight rads work and the bedroom one doesn't.

I've now bled every rad in the house twice, but no change. Eight are fine, one isn't.

Have I missed something depressingly obvious?

Thanks, Peter

P.S. I've also tried running the system with all rads closed down except the bedroom one. No change. *sigh*

[Roger Mills]

Assuming that both sides of the radiator are actually connected into the system (have you checked the pipework?) it sounds as if one of the valves is turned off, stuck shut or silted up. Have you checked that the lockshield isn't turned off? If so, have you bled each side in turn? [In other words, open the TRV and shut off the lockshield, and bleed. Then repeat the process with the TRV shut (preferably with the supplied plastic cap in place of the thermostatic head) and the lockshield open.] You should get a good flow of water from each side. [Before bleeding, set the CH zone valve to the manual position - or the 3-port valve to the mid-position, depending on what you have.]

[Tim]

I'd also give the TRV (the metal part at least) a bit of a wallop. Irrespective of the movement of the pin the valve jumper can stick on the valve seat inside the TRV.

Tim

[The Natural Philosopher]

The need for perseverance, and a trick

Turn the pump on flat out, and shut down every rad in the house on the balancing valves except the cold one.

Then bleed and keep bleeding.

It took me about 4 days to fully get the air out of a new installation.

Every time you repressure the boiler, air will come in in the water, and that has to be bled again.

[TheScullster]

"Peter Kemp" wrote

If all else fails (and bleeding the rad using each valve in turn is good advice) - close both valves, drain and remove rad. Check for sludgy stuff in rad and flush out till clean. Then (not sure about pressurised system method as I have open vented) open the offending rad valves in turn with suitable bowl handy and make sure you get decent flow. I suspect you may need someone to add water through the fill loop at this point if the problem rad is highest to check that both valves allow free flow. If nothing comes out of either valve, then you have either got a valve replacement job or a blockage.

I had a similar problem with 2 rads. Turned out there was some magnetite (main constituent of sludge) moving around, which stopped at a rad valve and completely blocked it. Sorted this by part opening the valve and "broggling" through the valve with a tie-wrap to clear the block until water flowed out. You should be able to see the internals of the valve operating by looking from the radiator connection end IYSWIM. As others have said you will need a plastic cap-type operating head for the TRV. Obviously need some dexterity juggling valves, tie-wraps and bowl here (plenty of towels advisable).

If you have similar blockage issues, make sure you fire through plenty of water into a bowl to clear all remnants.

HTH

Phil

[Peter Kemp]

Wow - some really helpful input and suggestions: much obliged.

I've re-bled all the radiators in the system. Each one now spits water the instant I turn the bleed valve, including the recalcitrant beastie, so I guess I can't blame an airlock.

Time for a slightly more 'assertive' approach, methinks...

Thanks everyone, Peter

[ARWadsworth]

The last time I came across this the lockshield valve was broken. It felt as if it was opening and closing but internally the valve had snapped and it was sat in the closed position.

Adam