Now that my hot water cylinder has corroded to the point that it leaks, I need to replace it (Cue for Rant: it was previously replaced in 1996 - I thought these should last as long as the house! what's the matter with modern cylinders ?). It's a standard copper, indirect, vented one with 28mm pipework for the gravity-fed heating coil. The return from the heating coil has a Drayton cyltrol mechanical valve, now well seized up, as they all apparently do, and no longer working. So while I'm changing the cylinder I'm thinking of adding a cylinder thermostat and a 2-port zone valve (to replace the cyltrol) e.g Honeywell L641 and V4043H. Hopefully it's a simple job to connect these to the programmer and won't affect the rest of the heating system (unlike converting the whole system to fully pumped).

Various potential snags come to mind. The pipe connections to the cylinder are 1inch parallel BSP, so will need some jointing compound. The old ones seem to use some sort of translucent silicone compound. I suspect PTFE tape won't be up to it. Any recommendations ?

When I fit a new (backup) immersion heater I'm a little nervous of using too much or too litte force (I suspect the old cylinder is now leaking due to the stresses caused by fitting the old i/h). Also, the immersion heater instructions say not to use any jointing compound, although plumbers always seem to use loads of putty for this job. What should I use, and how much tightening ?

When I fit the zone valve and thermostat I want to connect to the existing Potterton EP3000 controller (user guide long gone). I assume this should do the job if I can figure out the wiring. Any help available? Actually, the first problem will be getting the EP3000 off its backplate and getting at the connections - any advice ?

Reconnecting the heating coil will need some adjustment to the existing 28mm pipework, because the spacing between the connections is different on the new cylinder. Although I've done a bit of soldering of 15mm capillary joints in the past, I'm a little nervous of tackling 28mm. Would there be any problem if I dodge the issue and use multiple compression joints instead?

Are there any other potential pitfalls ?