central heating problem

[dihedral]

One rad in my elderly parents house does not seem to be heating up.
When the boiler, a new glow worm easicom 28 is fired up, all the other rads get hot but this one is cold on the bottom and only warmish near the top, even after an hour's boiler run time.

Have tried emptying the system down several times during other checks so there should not be any air locks. Have taken the rad to the garden and fitted a garden hose to it using a 3/4" bsp male and flushed through but minimal evidence of sludge.
Finally...when all other rads have the flow valve turned off, the rad gets piping hot and works as it should, sort of indicating gthe pipework is OK?
As soon as the other rads are re-introduced, this one goes cold. Have power flushed the whole system with no noticeable effect.
No amount of balancing seems to solve the issue either.
One final thing may be worth mentioning, when we first realised this rad was not heating up, we changed it out for a new type 22, its the only one in the whole house, all the others are old 30year+ single panel jobs.
Any ideas anyone please?

 

[swbjackson]

If balancing hasn't worked it's time to start looking for pipework issues.

 

[D_Hailsham]

One rad in my elderly parents house does not seem to be heating up. ...

when all other rads have the flow valve turned off, the rad gets piping hot and works as it should, ...

As soon as the other rads are re-introduced, this one goes cold. Have power flushed the whole system with no noticeable effect.

No amount of balancing seems to solve the issue either.

Everything points to the system not balanced correctly. Here's the Quick Method.

Your boiler is designed for a 20C drop between flow and return, which can be checked with Parameters d.40 (flow) and d.41 (return), so the LS valves will not need to be open very much.

 

[dihedral]

Thanks D_Hailsham, i will have another go at the balancing.

 

[Steelmasons]

Lockshield valves should be opened as much as possible in order to eliminate noise and at the same time adjusted for correct balancing ,systems that use a certain type of thermostatic radiator valve balance fine with all lockshield valves FULLY open , most systems will have a deltaT much narrower than 20c , good luck trying to maintain a temp differential of 20c cos it aint happening.

 

[dihedral]

Nothing like a bit of contradictory expert advice to throw the cat amongst the pidgeons

 

[Steelmasons]

Some do this job day in day out so i guess you could refer to me as the cat.

 

[dihedral]

I'm sittin' way up high on the fence on this one boys, watching to see if its fur or feathers flying Where's Mr.Hailsham?

 

[Steelmasons]

Is there a thermostatic valve fitted to the problem radiator? , have you checked the valve is fully open and not partially stuck shut?

 

[D_Hailsham]

Lockshield valves should be opened as much as possible in order to eliminate noise and at the same time adjusted for correct balancing.

Noise is a sign that the pump speed is too high. A correctly balanced system will often need the pump setting turned down.

Now I know this is impossible with the OP's combi boiler, which is why they suggest installing a flow control valve in the main flow or return pipe.

Systems that use a certain type of thermostatic radiator valve balance fine with all lockshield valves FULLY open

Which valve is that?

most systems will have a deltaT much narrower than 20c , good luck trying to maintain a temp differential of 20c cos it aint happening.

I agree that installing a 20C boiler into a system designed for an old 11C boiler can be problematic. But this is mainly caused by pipes which are now too large (flow rate halves when the differential doubles), so the LS valve has to be closed even more to achieve the required differential.

I should have said that the differential should not exceed 20C.

One thing to bear in mind is that a combi boiler is always sized for the HW requirement, not CH. This means that, in most cases the CH output of the boiler is much higher than necessary.

Use this Whole house boiler calculator to find out the CH requirement is for your house.

You can then set your boiler to this using parameter d.0.

 

[Agile]

One rad in my elderly parents house does not seem to be heating up.
When the boiler, a new glow worm easicom 28 is fired up, all the other rads get hot but this one is cold on the bottom and only warmish near the top, even after an hour's boiler run time.

So why did the boiler installer not balance the rads and sort out the problem?

Tony