problems with rads not getting warm??

[renton]

hi all.

im having a problem with the two main rads downstairs not heating up correctly.

they are both connected to the same set of pipes back to back on a wall.

both rads were removed to wallpaper behind them and then put back on .

now when the central heating is on these rads are not heating up as well as they should be or getting as hot as other rads in the house???

i have bled them time after time and there is defintaley no air in them.

the rads are cold at the bottom though and not the top???

i have tried balancing them which has improved things a lot but they are still luke warm at the bottom.

both rads ( one is brand new btw) have new trvs which seem to be working properly.

my boiler is a potterton envoy and im sure ive had a new central heating pump fitted less than a year ago.(it is set on number 3 which is the highest setting)

any ideas on what to try now???

would a more powerful pump work ??

thanks

steve

 

[JohnD]

the rads are cold at the bottom though and not the top???

Insufficient flow.

Verify that you have got the TRVs fully open and the caps are correctly fitted. and open the lockshields.

Close the other rads and see if these two heat up.

If so, balance the system by closing down lockshields on the other rads.

If you still have the plain plastic caps for your new TRVs, fit them and screw them fully down. see if this makes a difference.

 

[renton]

i have tried balancing the other rads in the house and it has made a big difference but they are still not getting as warm as the rest of the rads.

if i take the top off the trv the pin sticks up from the valve on the rad , i take it this means its fully open??

what difference will it make if i put the plastic cap on??

these rads are the two biggest rads in the system and also the furthest away from the boiler.

cheers

steve

 

[D_Hailsham]

Insufficient flow

Or too small a temperature differential - which is not the same thing.

If so, balance the system by closing down lockshields on the other rads.

But the only rads the OP removed and replaced were the two now giving problems. Unless the new rad is much bigger/smaller than the one replaced, there should be no need to change the LS settings on any of the other rads in the house.

If you still have the plain plastic caps for your new TRVs, fit them and screw them fully down. see if this makes a difference.

Of course it will make a difference -it will shut the TRV and rad off! So what does this prove?

Without doing a full rebalance of the system the following should help:

Remove the TRV head from both valves and shut both LS valves completely.
Open one LS valve about a quarter turn and allow rad to warm up.
Feel the rad pipes (one will be cooler then the other) and compare with a "good" rad.
If the temp difference is smaller than the good rad, close the LS valve a fraction (and vice versa), wait about ten minutes and check again.
When the temp difference feels about the same as the "good" rad, move to the other rad and do the same thing.
The adjustment on the LS valve should be very slight an eighth of a turn or less.

Of course, if you find that the other rads in the house have widely differing temperature differences between the in and out pipes, that suggest the whole system needs proper balancing.