1tim23 wrote:


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).

Is ther a 2-port valve on the heating side? If not you'll need to fit one,
and probably a bypass loop as well. If it's convenient to arrange the
pipework to use a 3-way valve and do a Y-plan system it'll be simpler.

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 ?

Boss white and hemp: that way if you susequently disturb the connection it
won't start to leak (inevitably at the bottom connection, requiring you to
drain down the cylinder again. Been there, done that :-(

Hint: use straight connectors, not elbows: you'll never get elbows to seal
and point in the right direction at the same time! You'll probably need 2
with female and 2 with male 1" BSP threads for the cylinder, and I'd use
22mm compression to the system.


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).

Why, is it leaking at the immersion heater boss?

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 ?

I use boss green, a ptfe-based compound, squished over the immersion heater
thread and fibre washer. Shouldn't need it but too many do :-(
For tightening (as for loosening) I think tapping the spanner rather than
exerting continuous force on it is more cylinder-boss-friendly.

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 ?

If you don't have a 'proper' wiring centre connecting it all together then a
12-way chock block in a 2-gang electrical surface wiring box with a blank
plate cover is a good place to bring all the system wiring together. Check
out Honeywell's wiring diagrams for S-plan (on the www) to see how it
should all go together.

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?

22mm should be enough if it's pumped - and easier to do. I'd arrange at
least one compression joint in each leg (ditto for cold water in and HW
out) which you can disconnect later if you need to, without disturbing the
joints on the cylinder itself.