Fitting a new radiator to an oil combi central heating system

[chopsaw]

I want to change a radiator on my combi based central heating syste

WITHOUT having to drain dowm the system. I propose to use a freezin mixture on the inlet and outlet pipes and then put the radiator i place. (The old radiator has already been removed and the pipe temporarily closed off.) My problem is will the pressure of the combi system blow the ice plug before I can attach the new radiator? Any comments gratefully received Thank

-- chopsaw

[Andy]

Why not relieve the pressure during the operation. I suppose there are various ways to do it, the most obvious being to press the overpressure relief valve button and shoot a few litres of CH water out of the overflow pipe. You can always repressurise it from the filling loop afterwards.

Andy.

[John Rumm]

I would not be so keen on that however. It only takes a small bit of crud to get lodged in the overpressure valve and you will have a leaking system. Better to save the overpressure valve for what it is supposed to do.

Draining a litre or two out of a drain point, a radiator tail connection, or even a bleeding valve will do the same trick.

[John]

NEVER open the relief valve unneccessarily. You have a major chance of it failing to reseat correctly with an ensuing slow pressure loss problem. The drain valve is the way to go. To the OP most oil combis have isolating valves between boiler and heating pipework. Shut these and open the air vent on the rad you are working on, catching the small amount of water released. this will have effectively depressurised the rads without affecting the boiler. If the old valves are good and the rad is the same size there may not be a need to do this. Only if you wish to change the valves or alter the pipes. Do one at a time or you may find the system empties itself around you.