CH pump and isolating valves.

I'm doing the exact same things tomorrow - the iso taps are leaking,and the householder wants it sorted now the Summer is alleged to be here.

Firstly I got a pair of iso taps from Screwfix:

I'm hoping they will be a straight fit onto the old pipes, but if not, then I'll just fit a short length of new pipe to one end of the existing pipes, then cut it to the right sized gap for the pump. The easiest way is to use a compression joint (around £3) to join the 2 bits of pipe if needed. Soldering is better, but not so easy on old pipe.

The pipes are likely to be 22mm. Only really old pipes are 3/4", anything after 1970 should be 22mm. If it is 3/4" pipe, then you can go to a proper Plumber Merchants to get some special olives, to allow the use of the 22mm iso taps with the 3/4" piping. These olives are slightly bigger on one side to get a good seal on the slightly smaller 3/4" pipe.

If you find that you need a bit of pipe, then you'd be best asking a local plumber if he'll sell you a short section, they always have short off-cuts, so that'd save you the £15 or so to buy a 3metre length, when

Pumps come in 2 or 3 standard physical sizes - the most common being 130mm between the two flanges to which the valves attach. So get a new pump which is the same size. With any luck, the new valves will be the same length as the old ones - measured from the flange to the compression joint - but it's as well to be prepared to remake one of the tails - just in case. [Maybe you can cadge some pipe offcuts rather than buying a 2-metre length].If you're particularly unlucky, the threads on the compression nuts may not be the same as the old ones - making it necessary to remove the olives and fit the new olives and nuts. Otherwise, you should be able to re-use the old ones.

Traditional pump valves are of the gate valve variety - which are a pain - so, if possible, replace them with valves which contain a quarter-turn ball valve mechanism.

It is common for the pump to be directly supported on the pipework - which is fine with rigid pipe. If you use flexible pipe, you'll have to support the pump some other way.