New radiator not heating up

[Zorro]

Hi
My house has five newish upstairs radiators and I just had nine new downstairs radiators fitted. Most of these are slightly higher rated than before. Before I had five upstairs and seven downstairs. The two extra radiators are fairly large compared to the rest.

When the heating is on, all the radiators bar one get hot so that I can't keep my hand on any of them. All the radiators have been bled and the pressure is fine. This radiator is one of the extra ones and probably the furthest away.

I have turned every radiator off except this one and even after about two hours it only becomes mildly warm. Again it didn't need bled. I will get back onto my installer but I would like some sort of understanding as to what might be the problem.

Any suggestions as to how to cure it?
Thanks
David

 

[Zorro]

Hi
My house has five newish upstairs radiators and I just had nine new downstairs radiators fitted. Most of these are slightly higher rated than before. Before I had five upstairs and seven downstairs. The two extra radiators are fairly large compared to the rest.

When the heating is on, all the radiators bar one get hot so that I can't keep my hand on any of them. All the radiators have been bled and the pressure is fine. This radiator is one of the extra ones and probably the furthest away.

I have turned every radiator off except this one and even after about two hours it only becomes mildly warm. Again it didn't need bled. I will get back onto my installer but I would like some sort of understanding as to what might be the problem.

Any suggestions as to how to cure it?
Thanks
David

Some more info, all the downstairs pipework has been changed from old microbore to new plastic flexible stuff. Wondered about increasing the pump flow or some sort of kink of the pipe below floors?

 

[Aire]

Are both valves on the problem radiator fully turned on?

 

[Zorro]

Yes, double checked. Definitely both on full.

 

[Zorro]

Radiators have all been fitted with a length of chrome pipe connecting to an elbow joint.

 

[Aire]

It should have a trv fitted, if it does take the trv head off and check that the pin pushes in and springs out freely.

 

[Zorro]

Fantastic! Just loosened the head and the radiator sprung into life. Took it off completely and the pin moves about 2-3mm. Not a huge amount but it seems to work fine.
Thanks very much Craig.

 

[Aire]

Great stuff, strange how it worked when only loosening the trv head though. It may not have been screwed on correctly or it's faulty. If the radiator stops working again then you'll need a new trv head.

 

[mubesjnr]

My fellow contributor Mr Craig Watson is indeed correct and I sincerely hope that this quick assessment and fix to the trv has resolved this issue for you.

That being said, as you allude to new rads being added to a circuit and pipe work being installed as well, you (or your installer to be precise) may need to ensure that this installation is balanced correctly. That is to say that the dynamic resistance across the installation is uniform.

Think of this as an example to demonstrate:
Take a simple c/h system consisting of a heat source (boiler) and two radiators of equal size and heat out put.
But one radiator is several meters away from the boiler compared to the other which sits adjacent to the boiler.
Both rads are piped in the same diameter tube and have congruent valves where both valves are fully open on both sides.
When the c/h is turned on for this simple circuit, the radiator closest to the boiler will become 'scorchio' and the one furthest away will remain cold, tepid luke warm....not as hot.
Why? Because of the dynamic resistance across the c/h system pipe work.
The hot water from the boiler will move across (through to be precise) the pipe work where there is least resistance. Hence, the need to balance the system by throttling one valve on the rad nearest the boiler (in this instance) to increase its dynamic resistance to closer match that of the rad furthest away on the long run of pipe work. Thus balancing the c/h system.
Unbalancing, a c/h system can also be caused by adding in a new radiator to an existing c/h circuit thus promoting the same condition as described above. Which in turn requires the c/h system to be re-balanced.

Hopefully, you only turned off your rads using the TRV's and not on both sides. If you turned off using just the TRV's for your test then the c/h system will remain balanced when turned back on. If however, you used both valves then you will more than likely need to re-balance the whole c/h system again.

More long winded posts can be given for balancing a c/h system if this is the case, but lets hope that as remarked at the top of my post, the expert analysis above has remedied it for you.

 

[Zorro]

Thanks for reply. The trv is definitely still not working correctly and I'll replace it. The input pipe to the radiator is very hot but the radiator is mildly warm even with the valves turned fully on at both sides. If I remove the head then the radiator comes on. I've done a rough balance of the system at the moment and will revisit it next.

 

[mubesjnr]

No worries...hopefully of help to you......if a little long winded I know. However, sounds like that TRV head needs replacing (just as the previous contributor assessed).
I would eliminate variables now and if you have the know how then balance the whole c/h system with the TRV head off of the troublesome rad and then deal with the TRV head issue once you have it at hand.

 

[Zorro]

Thanks

 

[Aire]

It's not unheard of for new trvs to be faulty, but just to be sure, does the valve body and trv head match the others on the system? If the wrong head is used on the wrong body, it won't work.