Rad not warming up

[thedigger]

We've recently had our CH system changed from a back boiler to a modern condensing boiler (with an unvented cylinder for the HW).

The existing pipework for the radiators is apparently a single pipe system - there are flow and return pipes going to the boiler, but they then deviate into different directions.

We had a load of building work done at our house, and every room was plastered. When the radiator was put back on, we replaced all the valves with Bulldog TRVs.

So, every radiator warms up except for one, in one of the bedrooms. I suspect this is the first radiator on the loop, if that makes any difference. We've opened the lockshield fully, doesn't make any difference. If we bleed the rad and let the water run out of it, the rad starts to warm up, but cools down again as soon as we close the bleed valve.

A plumber I asked seems to think the TRV and lockshield might be the wrong way round - the water seems to come in at the lockshield and out of the TRV (which I thought was normal?)

Any ideas?

<edit>

Btw, we didn't live in this house before the building work or boiler install were done, so no idea if this radiator got warm on the old system.

 

[PowerFlushAssociation]

Modern TRVs are bi-directional, so it does not matter on which side they are fitted. It is likely to installation debris stuck in one of the radiator valves. They should have power flushed the system to get it clean, it really matters on a one pipe system.

 

[thedigger]

Thanks for the reply.

The system was powerflushed for a few hours after the new boiler was installed. When the rads were taken off for the plastering, they were hosed through. Do you think it's worth using a pressure washer to properly blow the rad out instead?

 

[PowerFlushAssociation]

Power flushing uses:
- a power flush machine
- Magnets
- Chemicals
- Connects into system from one point
- Cleans the whole system from loose sludge

When you power flush you do not take off radiators and was them out.
This is also not called a power flush.
Taking of the radiators off and washing them, leaves the pipes and boiler full of sludge which can cause future problems on the boiler and system. All it does is "get rid of some sludge".
It is also worth stating that for the guarantee on the boiler to be valid (when it breaks down) your central heating water will be tested and it will fail the minimum water quality test, if all they did was take of and wash the radiators.

 

[thedigger]

Hi mate, it was definitely power flushed with a power flushing machine and with sludge removal chemicals. The rads were taken off after that so the plasterer could skim the walls and his labourer flushed the rads a second time with a hose. there was still some gunk in the rads when they were flushed a second time (its a pretty old house so I guess it solidified within the rad).

One more thing to add, I turned off all the rads except this one and that made no difference either.

 

[stem]

Try unscrewing the sensor head and removing it. This should put the valve into its fully open position. If it the radiator gets hot then, the sensor head is faulty.

 

[thedigger]

Thanks for the reply stem. I tried that, no luck.

I took the rad off, cleared it out with a pressure washer, tapped it with a mallet to loosen the sludge, pressure washed it again, until the water was completely clear. I then reversed the TRV and locksheild and filled up the system.

This radiator still doesn't warm up.

I'm not sure if it's wishful thinking, but the pipe where the locksheild is warms slightly while the heating is on, and the TRV pipe is stone cold still.

The only thing I can think is sludge where either the inlet or the outlet join the main 22mm pipe. Would another powerflush be the best thing to do now? Would turning off every other rad while doing the powerflush be a good idea?

 

[dcawkwell]

Thanks for the reply stem. I tried that, no luck.

I took the rad off, cleared it out with a pressure washer, tapped it with a mallet to loosen the sludge, pressure washed it again, until the water was completely clear. I then reversed the TRV and locksheild and filled up the system.

This radiator still doesn't warm up.

I'm not sure if it's wishful thinking, but the pipe where the locksheild is warms slightly while the heating is on, and the TRV pipe is stone cold still.

The only thing I can think is sludge where either the inlet or the outlet join the main 22mm pipe. Would another powerflush be the best thing to do now? Would turning off every other rad while doing the powerflush be a good idea?

Try turning off all the other radiators and see what happens.

 

[thedigger]

Done it already mate, didn't seem to make a difference. Is there a minimum time I should leave the others off for? I probably had the system running for an hour before my wife started moaning about the cold...

 

[xr4x4]

Did you try and open both valves to see if water came out when the rad was off?

 

[thedigger]

I drained the system (was swapping the valves over) so there wasn't a massive gush of water. Some water gurgled out of one of the pipes, and the other pipe had water sitting at the top of it. It didn't smell or look stagnant.

Not sure if this detail is relevant, but this rad is on the top floor, so is likely to be the first one in my system.

 

[thedigger]

Just done a bit more reading up on it... would there be any advantage to adding some additive to my system (X800?) and running it for a week to see if that clears the sludge.

 

[xr4x4]

Did the water come out brown or black?

 

[thedigger]

When I flushed the rad with a pressure washer - mostly clear, occasionally lumps of black sludge followed by a small amout of black water.

From the pipes while I was changing the valves - looked clear to me.

 

[xr4x4]

Allthough it might might help your system in the long term, I don't think it's going to sort your problem.