Downstairs Radiator/Heater Cold

28 Oct 2009
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United Kingdom
probly an amateur topic for the experts on here!!

I have;

Main HE24 Boiler (NOT combi but the otha one!)
Room thermostat
4 Radiators upstairs with TRVs
1 Radiator Downstairs with TRVs
Grundfos 15/60 pump
Siemens 3 way valve (newly installed)

Three upstairs rads closest to the pump warm up. the 4th upstairs rad not warming up and nor is the downstairs rad. Also hot water is working fine.

I have bled the radiators and pump with only water coming out now. It hasn't made a difference.

I had a suspicion it might be the pump so i removed the big screw at the front and stuck a screwdriver in there to see if its still turning over. It is turning over.

I have tried to balance the system, stil making no difference??

Any suggestions??
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i also removed all the TRV's incase they were faulty. It didn't make a difference.

close all the hot ones and see if the cold ones heat up.

Report back with results.

Especially if the upstairs and downstairs rads are hot all over, or hot at the top, or hot at the sides and top, or hot at the bottom only


Too slow :mad:
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A 24 kW boiler for 5 rads? :eek:
Has it ever worked properly?
When did the problem start?
the boiler was installed two years ago and it has worked properly since.

it started giving me a headache about 2 weeks ago when I switched it on after a long summer!

I am closing the hot rads to see if tht works.

hey bengasan...

is this boiler too excessive for the amount of heaters???

or not excessive enuff??
if closing the hot ones doesn't make the cold ones heat up, look carefully at the TRVs on the cold rads after you have taken the heads off. Look for a steel pin sticking up. Is it?

If not you can try pressing it down and seeing if it will spring up (use a teaspoon on something as you need more pressure than your thumb can give). Don't bend them sideways or pull them out.
"Standard" or average rad is about 2 kW, times 6 (5 mentioned plus assuming 1 without trv) would make about 12 kW, which would mean twice the size you need.

As I always use independent timers that allow you to never have the ch and dhw on at the same time, I don't add the dhw need to the calculation.
In the old days, the cylinders had a low heating requirement and the timers did not allow total separation, hence the standard practice in those days to add 3 kW for dhw to the ch demand.
Modern cylinders can absorb 10 - 20 kW, and should be able to reheat in about 20 minutes, which is why they should be heating up when the ch is off.

its worked, the cold rad has heated up!!

im guessing its a balancing problem. wts the best way to do this?? thermometers?
To make sure your boiler actually works in condensing mode, it really should be balanced properly, which means you need clip on thermometers, or i.r. model.
Flow and return should have about 20 degrees C difference with the boiler set at 80C.
thank you all for your help and advice.

I finally have all the heaters working again. I have roughly balanced them until i get a hold of sum thermometers.

Any idea how much they retail for in the UK and the best websites/shops to buy/hire from?
I think mechanical ones ( bimetal clipon model) are about 20 quid, plumbers merchants would have them.
open the others about a quarter-turn only at the lockshield. Balancing only need them open a tiny amount.

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