Faulty TRV??

[ally81]

Hi - I've recently had my integral garage converted into a habitable room and the radiator that was fitted has been supplied from the hallway radiator that doesn't have a TRV, but as I understand it is controlled from the thermostat which is also in the hallway. My issue is that the new radiator only comes on for a short period when i put the heating on and then turns off despite all other radiators in the house, including the hallway staying hot. The TRV on the radiator in the garage conversion is turned up full however the only way I can get it to stay hot is to turn the thermostat temperature up further.

Does this sound like an issue withe the TRV that has been fitted - it is definitely a cheap part that has been fitted?

Thanks!

 

[Armo74]

What type of system do you have? Boiler make and model?
Could be a balancing issue, could be a few things.

 

[ally81]

I have a combi boiler - Ideal Isar. What's the best plan then?

 

[Armo74]

How many rads do you have? how big is the new rad? what size pipe has been used? does the pin on the TRV push up and down if you remove the head? Does the pipe leading up to the TRV get hot or just warm?

 

[ally81]

10 radiators, including the new one. New radiator is single 1200mmx500mm, pipe is 10mm and gets hot and yes i can move the pin (although not that easily)

 

[Armo74]

sounds like there is something restricting the flow through the TRV if you say the pipe gets hot leading up to it,could possibly be faulty wouldnt be the first time. A good test would be to take the rad off and open the TRV into a bucket,not ideal but a good way of checking.

 

[ally81]

the radiator itself also gets hot, it just doesn't stay hot.

 

[Armo74]

Does the room get hot enough? Was the radiator sized correctly?

 

[ally81]

No the room does not get hot enough, it turns off before it reached the correct temperature. As an aside, I think the radiator may also be undersized which I'll need to argue with the builder over.

 

[Armo74]

I normally calculate the size myself but you could try radcalc.com i think it's called to see what size you should have in there, with it being a garage conversion unless insulated correctly you could have a fair amount of fabric heatloss.

 

[ally81]

It is undersized!! Would an undersized radiator effect the symptoms I've described - with the radiators getting hot but not staying hot?

 

[Armo74]

If all the other rooms are reaching the correct temperature and the radiator in the the conversion is getting hot but the room is not reaching temperature it is undersized, and i suspect the thermastat is getting satisfied and shutting the heating off Ideally the new radiator should have been teed off from the main flow and return pipes if it is a long run from one to the other if you say the new pipe is 10mm. Is the TRV set to the full amount?

 

[ally81]

If by set to the full amount you mean turned up full then yes it is. It may indeed be teed off the main flow as the main feed to the hall radiator was exposed when opening up the wall to create the doorway and the feed was taken from there.

So does it sound like it's likely that its all because the radiator is too small then?

 

[Armo74]

It could be but difficult to say without room dimensions,window dimensions, U values etc. But if the room is not reaching temperature even with the TRV set on full and the room stat on full then it is a strong possibility.

 

[D_Hailsham]

If the rad is undersized the TRV will stay open because the room will not get up to temperature. Remove the head from the TRV and see what effect it has.

If you can get the rad to stay hot by turning the thermostat up to 25, the reason it gets cold is the stat is turning the boiler off.

The complete system will need balancing. You can't just add another 1kW rad (what yours is) and hope it will work correctly.