Some radiators fail to heat

[gboyd]

Hi all,

My first post on the forums and rather predictably it is to beg for your advice with an issue I have encountered with my heating system.

Firstly let me apologise for the length of this post, I want to give as much detail as possible.

I will try to summarise the issue along with what I have tried to resolve with no success.

This is a fairly new system installed approximately 6 years ago although I only moved into the property 2 months ago.

In my house I have a total of 9 radiators.

Of these 9 radiators, 6 of them heat perfectly to the point which they are too hot to touch. Perfect!

However, the other 3 radiators only heat to ‘luke’ warm and not enough to give off any heat and are as good as useless.

For the 3 affected radiators, I have replaced the temperature valve on the inlet and the lock shield on the outlet pipe. I have removed each radiator in turn from the wall and drained fully checking for blockages but both the water and the pipes are clear.

When the heating is turned on, the inlet pipes get very hot delivering the hot water without any issue. When I keep the outlet pipe disconnected the hot water coming from the inlet pipe flows straight into the radiators and out the other side so I have eliminated the flow coming into the radiator (which is hot) and the radiator itself as the problem.

When the other 6 working radiators are turned on you can instantly hear the flow of hot water entering the radiator and being circulated through and out the other side. With the 3 faulty radiators this sound of water flowing does not occur despite the inlet pipe heating up.

This affects 2 radiators downstairs and 1 radiator upstairs.

My system is run by a gas combi boiler which heats the water on demand in a sealed system. Apart from when replacing the water in the radiators I drained, the pressure sits at a constant 2 bar which I believe is correct from the FAQ. I really don't think this is causing any issue as the inlet pipe does deliver hot water (from feeling the inlet pipes are red hot) to all 3 problem radiators.

Without trying to lead any of the experts here towards the issue I certainly seem to think it resides in the flow of water through the outlet pipes. Its almost like the water can't flow through the outlet pipes, despite confirming 100% that they are completely open and replacing them with new lock shields.

I have also had the system professionally balanced whilst the above work was being carried out.

All 9 radiators have been bleed and I have tried shutting all radiators off leaving just the offending 3 but this has not helped.

Nothing has resulted in any progress ....

So please, can anyone help me solve this problem or give me anything to try or even what I should do next? I am desperate to get these radiators working again.

Kind regards,
Graeme

 

[Bahco]

Turn all rad valves to 1 quarter turn open and offending ones 1 full turn open.

Also drain your boiler to 1 bar too.

Worth looking at FAQ no 8 for rad problems.

 

[gboyd]

Sorry mate, I was constantly updating my post as I read through the FAQ to make sure I let you guys know what I had tried.

I did close off (and many variations of this) all rad valves and this resulted in the inlet pipes to the 3 faulty rads getting ridiculously hot but still no flow to speak off.

I have read through the FAQ but I don't think there is anything I haven't tried

I will drain the system a little to return the boiler pressure to 1 as advised.

 

[Bahco]

I did close off all rad valves and this resulted in the inlet pipes to the 3 faulty rads getting ridiculously hot but still no flow to speak off.

Flush out rads and ensure valves and trvs are opening.

 

[gboyd]

Sorry mate, that reply lost me a little.

By flush out rads do you mean open the first rad from the boiler that has the extra little nozzle and drain the whole system again?

This was done yesterday by the plumber I got round but apologies if this is not what you meant.

The 6 working radiators were not touched but the 3 that don't heat were drained completely, taken off the wall, cleaned by flushing boiling water from my kettle through them and the water was passing without problems and very clean.

The outlet valve was opened fully and the inlet valve with the temperature control was set to 5.

Does this cover your advice above?

 

[Bahco]

Does this cover your advice above?

Yes but would have flushed them with a hose.

Is it a microbore pipe system by any chance. If not follow the the feed pipes to where they join the main pipes and tell us how they have been piped.

 

[gboyd]

Also, just to say the plumber fitted new Danfoss tvrs and lockshields to the 3 faulty rads and said they were good valves and thought that would have solved the issue.

When it didn't and he then drained and removed the 3 rads to flush them he doubted that would be the cause due to the system being so new and of course this was correct.

He then spent approx 3 hours trying to balance the system by running around adjusting all of the rads around the house by different amounts.

He tried various different boiler pressures too.

At the end he said he had never come across this before and was totally stuck for what to try next or what the problem could be after elminating everything he had seen before.

 

[gboyd]

Does this cover your advice above?

Yes but would have flushed them with a hose.

Is it a microbore pipe system by any chance. If not follow the the feed pipes to where they join the main pipes and tell us how they have been piped.

Sorry mate, now I'm totally lost. I don't know what type of pipe system is installed nor do I know how to follow the feed pipes to where they join the main pipes

The boiler is wall mounted in a cupboard on the way up the stairs and the pipes feed directly out the bottom of the boiler and then disappear. Only time I can see the pipes again is when they come out the wall at either sides of the rads

 

[Bahco]

Is it a microbore pipe system by any chance. If not follow the the feed pipes to where they join the main pipes and tell us how they have been piped.

 

[gboyd]

Our posts overlapped.

I have responded to your original post above your re-post.

 

[Bahco]

How big are the supply pipes

 

[gboyd]

I'm at work so can't give an accurate figure but from memory I would estimate they are 15mm.

Thanks for your time so far Bahco

 

[gboyd]

Anyone think it could be a physical blockage in the outlet return pipe?

I really hope not as only 1 of the 3 rads have the outlet pipe coming from the floor, the other 2 come out of the wall horiziontally and then turn vertically like an upside down 'r'

Although, with that said, could that be possible when the radiators with issue are not sequental i.e. one in a bedroom and one in a livingroom downstairs then one upstairs hall? And if it was the return pipe, can the the fact that the other 6 all flow perfectly be explained?

 

[D_Hailsham]

Its almost like the water can't flow through the outlet pipes, despite confirming 100% that they are completely open and replacing them with new lock shields.

But all you prove, when you disconnect the rad from the LS valve, is that water flows into the rad and out again. That proves nothing about the pipe after the LS valve.

I have also had the system professionally balanced whilst the above work was being carried out.

He then spent approx 3 hours trying to balance the system by running around adjusting all of the rads around the house by different amounts.

That does not sound very "professional" to me
Did he remove the TRV heads while balancing?
Did he use thermometers to measure flow and return temps, or just do it by feel?
Did he balance the rads in the correct order (nearest pump first then work away)?

All 9 radiators have been bleed and I have tried shutting all radiators off leaving just the offending 3 but this has not helped.

Have you tried closing down all rads, then opening one faulty rad at a time to see what happens? If they get hot, then it is a balancing problem; if not, you have a blockage in the return from the LS valve.

 

[D_Hailsham]

Although, with that said, could that be possible when the radiators with issue are not sequental i.e. one in a bedroom and one in a livingroom downstairs then one upstairs hall? And if it was the return pipe, can the the fact that the other 6 all flow perfectly be explained?

Don't forget that radiators are in parallel, like the rungs on a ladder. The main pipes (the sides of the ladder) may not be blocked but the short length of pipe from the rad to the main pipe (part of the rung in my analogy) may be blocked.

You should be able to check this as follows:

Shut off both rad valves (does the TRV close valve completely? if not insert a coin inside head and close carefully until it stops)
Disconnecting the LS valve from the radiator and drain rad
Turn system back on
Open LS slowly.
If the pipe is clear you will get water flowing out of the LS valve rad connection.