FITTING THE PUMP
Either your first or second section of radiator pipework — the pipes that run from the boiler to the radiators — will take you up to the position of the pump specified on your plans. Fitting this requires some care.
Pumps come with two fittings, one for each end. These are different from those used in other parts of a plumbing system — one end has a standard compression joint, for connecting to the pipework, but the other has a flat flange which makes it easy to slide the pump out when it needs repairing or replacing. You cannot use jointing compounds to make a watertight joint between the flange on the fitting and that on the pump — you have to rely on a thin sealing washer — so it’s vital that the pump, and the pipework on either side of it, are accurately in line.
Follow the instructions provided with the pump carefully — some have to be fitted in particular orientations. Clip the pipework just either side of the fitting so that the pump is supported properly. Compressionjoint the fittings to the pipes, but only handtighten the cap nuts, and do not apply any jointing com pound. Then slide the pump between the flanges, with the sealing washers in place. Loosely screw up the flange nuts and check that all the pipework is of the correct length and accurately aligned.
For the time being, remove the pump and its unions and replace it with a short piece of pipe held in place with normal straight compression couplings. This ensures that no debris gets into the pump when you flush the system later.
It i’s best to install the pump and its pipework on either side early on, rather than leaving it till last — doing it that way, you almost certainly wouldn’t get as accurate a fit.
Fitting a piece of pipe in place of the pump isn’t easy — there isn’t enough slack to get normal compression couplings over the pipe ends. If you can find them, use slip couplings which slide over the pipe.