Stone cold radiator - tried just about everything!

[Hooky]

Can anyone help?
I have a stone cold radiator which will get slightly warm if you shut off all the other radiators then once you open the others it goes cold again. The exit pipe from the radiator never gets hot. I have bled the system and balanced it, replaced the pump and am at a loss as to what could be the problem. A heating engineer has told me that there must be a blockage in the pipe from the radiator and wants to repipe the radiator. We have drained down the radiator, there was a little sludge, it is only 7 years old. We have also opened the exit valve and water poured out from the pipe that we have been told was likely to be blocked. Would this happen if the pipe was blocked? Any ideas as I really don't want to go down the repiping avenue unless its the last resort. We have microbore piping downstairs and standard upstairs. It is a fair way from the boiler and did work when we first moved in. Oh and it is a Worcester bosch combi boiler.

 

[daveaf]

The radiator may still be partially blocked. But still has enough let by to gradually fill up over time. Have you tried to remove it and take it out in the garden and put a hose pipe up its arse to see if the water flows through it??

Whilst it is off, you could also try and open ~BOTH the radiator valves and see if water comes out of those, this would prove if either the feed or return pipe was blocked.

Another thing you could try is to shut off the other rads and set your pump to max speed to see if you can push the blockage out, The only downside with doing this is that you will just push all the silt etc back into the system and it should ideally be removed.

REmoving a radiator is very easy to do, this would be my first port of call.

 

[namsag]

Yep easy mistake to make is to think return is blocked because the flow gets warm. If flow is partially blocked it will let enough water through to warm pipe but not enough to heat rad etc.
So as been suggested open both valves with rad removed and try the flow with the heating motorised valve in manual position

 

[daveaf]

Dont worry about touching the motorised valve. Just shut off and remove the faulty radiator and try flushing it through. You can then also open the valves up 1 at at time and see if water comes out of those. The water can either be collected in a bowl, or:

If you have an outside tap with a screw on hose pipe spiggot, you can use this and connect a hose to the valve as both threads are 3/4" BSP Ive used this method in the past to drain the system down too.

 

[daveaf]

Oh and you will obviously have to make sure that the room stst is high enough that it is calling for heat to the rads!!

 

[Hooky]

We did remove radiator and flush through. We have checked exit pipe and it flowed with water, only thing we didn't do is the inlet pipe because it seemed to get hot. We'll give it another go. If that flows fine I am a loss as to what it could be. We have checked valves etc. Watch this space!

 

[namsag]

If he is opening the flow valve to rad without the heating motorised valve being open he may not get the correct flow out , Same as you have to have it in manual position to drain a system properly

 

[daveaf]

If he is opening the flow valve to rad without the heating motorised valve being open he may not get the correct flow out , Same as you have to have it in manual position to drain a system properly

I know thats why I suggested that he made sure the room stat was set high enough that the 3 way valve would be directing water to the rads.

 

[Hooky]

Do you mean put the heating on while opening the valve. If so should all the other radiators be shut off?

 

[daveaf]

No, you need to leave the system in full operational use with all rads in service with the heating on and then just work on the one with the problem.

If all the rads were shut, the water would not circulate and the boiler would cut out on over heat.

 

[stationapproach]

Hi daveaf:

if all the other rads were closed, then as long as the system had a 3port mid position valve or an auto bypass valve and circuit, then the boiler should not overheat, the water pressure would open the bypass valve and the water would flow through this circuit instead.

 

[JohnD]

if you suspect a sludge problem, start by giving it a chemical clean with Sentinel X400 or similar. This will cost you £15 at the plumber's merchant or DIY shed. As long as there is enough flow for it to circulate, it will loosen sludge. You can leave it in the system for up to 4 weeks, working normally, preferably with the pump on high, before draining and rinsing. You will know it is working if the water quickly goes inky black (this is the sludge being loosened and carried round in the circulating water. If you can afford an extra £100 and do basic DIY plumbing fit a Magnaclean as well, I promise you will be amazed and delighted to see how much sludge it traps.

Closing the hottest radiators some of the time, or balancing, will force more of the flow through the cool parts, thus improving the cleaning action there.

 

[Hooky]

Took the radiator off again drained it ran water through, sludge came out but is now clear. Put on heating and opened both valves both (while radiator was removed) of which flowed well while discharging sludge into a bowl. Put the radiator back on, bled system and still the flaming thing doesn't work! The radiator in the room above also seems to be having trouble heating. Is the only solution to repipe or is it worth putting in a sludge remover even though the heating doesn't seem to get to the problem radiator? If we were to use a sludge buster thing how do we put it into the system on a combi boiler?

 

[JohnD]

Is the only solution to repipe or is it worth putting in a sludge remover

No, yes.

As you are comfortable taking radiators off, you can empty that one, and then, while it is empty, take out the vent plug and pour it in using a funnel and small hose. Or you can buy an injection kit if you prefer to squirt it through the vent hole.

Or if you have drained the system you can take off an upstairs rad valve and pour it down the pipe.

Have you balanced the system yet?

 

[gigz]

Close all other rads, take off problem rad, connect hosepipe to one of the valves, then open it and flush till waters clear (have someone operating filling loop, keeping pressure at about 2 bar) Then transfer hose to other valve then repeat. Once thats clear drain down all other rads and refill, turn off all rads again to push water to the problem rad. If its working now, as suggested add some x400 and run for 4 weeks (turning odd rads off so it gets to the whole rad system) Drain down again and add x100 and balance system. You could try back-filling through the valves but this can be messy.