Continued Central Heating Problem

[BSAvale]

I have spent hours this morning try to fix this issue, I have asked on here about it before and tried most things, I have a had a plumber round who wasn’t terribly useful either. I am not a plumbing expert but pretty competent at DIY and fault finding but I am a bit stumped now.

We have 20 radiators in our house, the one in our bedroom does not heat up properly, to such as extent that it is cold in there and we have switched rooms. We have a large Bosch combi boiler and Hive thermostat.

The radiator gets warm at the top, only warm, not very hot. There is hot water at the lock valve as the pipe is hot. Radiators in the whole house have been bled and the boiler re-pressurised, TRVs have all been checked and no stuck pins are present. Based on the logic that hot water gets to the offending radiator, the plumber replaced the lock valve. Radiator did not get hot.

This morning I have removed the radiator and lugged it outside and flushed it through with the hose - some black gunk came out and I thought great, maybe that was the problem.

Radiator re-fitted, boiler re-pressurised and all other radiators turned off….the radiator got much hotter than it used to, but not a uniform heat distribution within radiator. This is with the lock valve fully open and the TRV on full. Pipe at lock valve is hot, pipe at TRV isn’t which I suspect might be a key symptom? I thought the problem was close to being solved to went around turning other radiators back on….bedroom offending radiator cooled down quite a lot.

I then decided it is likely a balancing problem…I went around the house and halved the amount the lock valves were open on every other radiator to bodge more hot water distribution to the offending radiator…it still didn‘t get as hot as other radiators, but what I did establish is that the lock valve position on some of the radiators is very sensitive with very little rotation going from cool to very hot radiators.

The two radiators in the hallway are roasting hot with the lock valve barely open and the control valve also barely open.

The offending radiator is in a room which was the newest extension on the house - so I am wondering if there is a piping issue or whether it is just a case of it must be the furthest from the boiler and so it remains a balancing issue. I plan to try to balance the whole house next weekend properly with the whole 12C delta across each rad starting at the one that heats up fastest…this is going to take ages - before I do that, anyone with more plumbing expertise that me (which is most people) got any other ideas? Could the radiator itself be at fault? I didn‘t want to spend £150 on a new radiator for it to have the same behaviour.

Floor plan below, boiler is in the utility room, radiators all marked in red, offending rad highlighted in yellow with the green showing the newest part of the house so assumed to be furthest on water circuit from boiler.



Any suggestions much appreciated before I spend days trying to get the balancing right!

thanks in advance.

BV

 

[bullet chucker]

Try banging the boiler right UP to max, is the pump duel speed? With the max temperature it might force' the circulation with all valves fully open.

BC.

 

[BSAvale]

I did try turning the heating system temperature up but I didnt put it to max, I will give that a try.

I don’t know about the pump, I will try to find out.

thanks for the tip

 

[jcampbellsmith]

Is your boiler rated for 20 radiators? I once had a dodgy radiator and eventually found a bit of gravel in the microbore pipe feeding the radiator. I would be looking closely at the new pipework and how it's been joined in to the original pipework.
Regards
JCS

 

[NullMac]

some black gunk came out and I thought great, maybe that was the problem

some...not necessarily all

Radiator re-fitted, boiler re-pressurised and all other radiators turned off….the radiator got much hotter than it used to, but not a uniform heat distribution within radiator.
I then decided it is likely a balancing problem

Why? If there is water getting to the radiator it should heat up uniformly irrespective of the balancing of the system. This suggests that there is an issue with the radiator, no ?

If I were you I would swap radiators around. See if this radiator works properly somewhere else in the system and see how a radiator you know works gets on in the problem location.

 

[fallow me]

I would investigate the pump, had a similar problem a few years ago, it turned out to be the pump had failed

 

[dlz90]

You have already tried to balance the system so I'm not telling you to suck eggs here,anyway it goes something like the following you need to find out which rad gets hot water first then the second and so on, lockvalves in the first opened a little the second rad a little more and so on the last rad should be nearly full open the idea radiators closest to the boiler shouldn't be taking the bulk of the hot water.

And something else pump speed settings try putting it up to max if it isn't already, or turning it down experiment till you see results hopefully.

D

 

[BSAvale]

some...not necessarily all

Why? If there is water getting to the radiator it should heat up uniformly irrespective of the balancing of the system. This suggests that there is an issue with the radiator, no ?

If I were you I would swap radiators around. See if this radiator works properly somewhere else in the system and see how a radiator you know works gets on in the problem location.

I flushed the rad with the hose in all orientations until it ran clear for a while, agreed though, could still be a gunk issue.

I had exactly the same idea to move the radiator to see if the issue follows the radiator or stays in the room but annoyingly none of the others are the same size so the pipe work won‘t easily fit.

 

[BSAvale]

Is your boiler rated for 20 radiators? I once had a dodgy radiator and eventually found a bit of gravel in the microbore pipe feeding the radiator. I would be looking closely at the new pipework and how it's been joined in to the original pipework.
Regards
JCS

Whilst I cannot find the rating for the boiler in terms of rad qty, it is the largest Worcester Bosch combi and the people I bought the house of 2 years ago didn‘t penny pinch on anything so I suspect it is more than adequate.

 

[FoxAndDeer]

I had a similar issue, albeit on a smaller central heating loop than yours.

I bought a radiator flusher product from Screwfix. My logic being - I can clear gunk out from the rads, but there could be gunk in pipes / valves around the system.

Left the cleaning agent (which dissolves gunk) in the system for a week (longer than they recommend), then a total drain and refill of the entire system. Water that drained out was minging.

Problem solved instantly - put plenty of inhibitor when I refilled.

This is the stuff I used: Sentinel X400 System Restorer 1Ltr

Obviously no tie to that product, but it worked for me.

 

[BSAvale]

I had a similar issue, albeit on a smaller central heating loop than yours.

I bought a radiator flusher product from Screwfix. My logic being - I can clear gunk out from the rads, but there could be gunk in pipes / valves around the system.

Left the cleaning agent (which dissolves gunk) in the system for a week (longer than they recommend), then a total drain and refill of the entire system. Water that drained out was minging.

Problem solved instantly - put plenty of inhibitor when I refilled.

This is the stuff I used: Sentinel X400 System Restorer 1Ltr

Obviously no tie to that product, but it worked for me.

That’s interesting…I will look into that.

Is your boiler rated for 20 radiators? I once had a dodgy radiator and eventually found a bit of gravel in the microbore pipe feeding the radiator. I would be looking closely at the new pipework and how it's been joined in to the original pipework.
Regards
JCS

I have just done some sums on this…boiler is rated at 42KWh, spec sheet says capable of 30KWh heating - EDIT - to add, I have just been into the boiler setting to make sure it wasn’t down rated and it is set at 74% which is very close to my calcs so it is set up correctly,

House heating requirement based on volume and the various coefficients factored in is just under 20KWh so the boiler is more than capable which is good to have calculated.

Try banging the boiler right UP to max, is the pump duel speed? With the max temperature it might force' the circulation with all valves fully open.

BC.

Just done that…rad in question is very hot at the top but cool at the bottom, all the other rads in the house almost too hot to touch as expected with heating system water set to 90C…So now I am suspecting the radiator again!

 

[FoxAndDeer]

That’s interesting…I will look into that.



I have just done some sums on this…boiler is rated at 42KWh, spec sheet says capable of 30KWh heating - EDIT - to add, I have just been into the boiler setting to make sure it wasn’t down rated and it is set at 74% which is very close to my calcs so it is set up correctly,

House heating requirement based on volume and the various coefficients factored in is just under 20KWh so the boiler is more than capable which is good to have calculated.



Just done that…rad in question is very hot at the top but cool at the bottom, all the other rads in the house almost too hot to touch as expected with heating system water set to 90C…So now I am suspecting the radiator again!

Hot at the top cold at the bottom matches my radiator issues - sounds like gunk!

 

[BSAvale]

Having left the heating on boost for longer, the misbehaving radiator is now nice and hot with no cold spots…since all I did differently was turned the boiler heating system up to max temp, that must have been what cured it.

Whether it will work tomorrow with the boiler turned back down we will see.

Thank you for the collective help SD…

BV

 

[kennyc]

if the TRV is cold and the lockshield hot, its possible that **** has built up on the TRV passageway, worth isolating the rad and flushing the TRV backwards into a bucket.
if you want to eliminate balancing as the cause just turn off all the other rads and see if the rad in question heats up, its not unkown to get a soft sludge build up in a slow moving pipe so it may be that if you are lucky. again you can often clear these by flushing into a bucket, do both ends.

 

[BSAvale]

if the TRV is cold and the lockshield hot, its possible that **** has built up on the TRV passageway, worth isolating the rad and flushing the TRV backwards into a bucket.
if you want to eliminate balancing as the cause just turn off all the other rads and see if the rad in question heats up, its not unkown to get a soft sludge build up in a slow moving pipe so it may be that if you are lucky. again you can often clear these by flushing into a bucket, do both ends.

That makes a lot of sense - is that TRV off, or just disconnect it from the radiator and then open it with a bucket ready?

Already tried the all rads off and it got warm but not very hot, this was prior to flushing it this morning though.

 

[bullet chucker]

If as you say ALL' the rads are hot then circulation seems ok' I would isolate (turn off) the suspect rad and check how the system performs. Then you may only have to replace that one rad. When I had our new boiler fitted I requested a reverse flush to the entire system then refilled with inhibitor.
YOU BEAT ME TO IT WRITING THIS. Good luck.

BC.

 

[kennyc]

Having left the heating on boost for longer, the misbehaving radiator is now nice and hot with no cold spots…since all I did differently was turned the boiler heating system up to max temp, that must have been what cured it.

Whether it will work tomorrow with the boiler turned back down we will see.

Thank you for the collective help SD…

BV

sounds like poor circulation, your balancing may have helped the problem, you may even have shifted a blockage, turn the temp down as it will help the efficiency of the boiler , ideally you want a 20C delta T across the system, any uncontrolled rads will probably need shutting down considerably, take the TRV heads off before balancing

 

[kennyc]

That makes a lot of sense - is that TRV off, or just disconnect it from the radiator and then open it with a bucket ready?

Already tried the all rads off and it got warm but not very hot, this was prior to flushing it this morning though.

just shut both valves, drain the rad and swivel both valves away from the rad into the bucket

 

[Sharpie]

Just done that…rad in question is very hot at the top but cool at the bottom, all the other rads in the house almost too hot to touch as expected with heating system water set to 90C…So now I am suspecting the radiator again!

I haven't looked more than a few posts in (lifes too short) but your radiator should start off hot at the bottom, then cooler towards the top. That's if it has been done properly, i.e. flow into the bottom, return should be at the top, meaning a long pipe. Lockvalve on inlet (flow, at the bottom), TRV on outlet at the top, where it is conveniently positioned to adjust without stooping down.

This gets the best out of any radiator.

Sure, far too many installations have both valves at the bottom, thereby wasting a lot of their capability.

Installing them with the outlet at the top and inlet at the bottom is best, but some don't like to look at the exposed vertical pipe leading to the top.

Hot water rises. Pump it in at the bottom, suck it out at the top.

An infrared thermometer waved over the thing will show you the temperature distribution, whether the flow and return are connected backwards, whether there is air in the top (so cold) and it's time to bleed, etc.

Of course your pump has to be up to the job, and is unlikely to be able to move the water around sufficiently if the balancing valves are open too far.

Depending on the lay of the pipework, and its sizing, it may be that there is far more black crud blocking up the pipes than the rads. By the time you find loads inside the rads, having taken them off and flushed them, your pipework could be far more badly clagged up. TBH flushing the pipework through properly is best left to a professional, it's not as easy as just connecting a hosepipe to one end and letting it run.

As I said, I don't have time to read this all the way through, so if these basic principles have not already been discussed, that's my pennyworth.

 

[User00036]

If its a rust problem in that rad, try moving a bloody big magnet up & down the outside. Your thermal might be useful.