Ho****er cylinder replacement & control upgrade - advice please

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 199 - I thought these should last as long as the house! what's the matte with modern cylinders ?). It's a standard copper, indirect, vented on with 28mm pipework for the gravity-fed heating coil. The return fro the heating coil has a Drayton cyltrol mechanical valve, now wel seized up, as they all apparently do, and no longer working. So whil I'm changing the cylinder I'm thinking of adding a cylinder thermosta and a 2-port zone valve (to replace the cyltrol) e.g Honeywell L641 an V4043H. Hopefully it's a simple job to connect these to the programme and won't affect the rest of the heating system (unlike converting th whole system to fully pumped).
Various potential snags come to mind. The pipe connections to th cylinder are 1inch parallel BSP, so will need some jointing compound. The old ones seem to use some sort of translucent silicone compound. suspect PTFE tape won't be up to it. Any recommendations ?
When I fit a new (backup) immersion heater I'm a little nervous o using too much or too litte force (I suspect the old cylinder is no leaking due to the stresses caused by fitting the old i/h). Also, th immersion heater instructions say not to use any jointing compound although plumbers always seem to use loads of putty for this job. Wha should I use, and how much tightening ?
When I fit the zone valve and thermostat I want to connect to th existing Potterton EP3000 controller (user guide long gone). I assum this should do the job if I can figure out the wiring. Any hel available? Actually, the first problem will be getting the EP3000 of its backplate and getting at the connections - any advice ?
Reconnecting the heating coil will need some adjustment to the existin 28mm pipework, because the spacing between the connections is differen on the new cylinder. Although I've done a bit of soldering of 15m 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 multipl compression joints instead?
Are there any other potential pitfalls
-- 1tim23
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1tim23 wrote:

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.

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.

Why, is it leaking at the immersion heater boss?

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.

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.

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.
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snipped-for-privacy@ntlworld.com Wrote:

It suddenly started leaking near the IH boss for no apparent reason after not being touched for 9 years. A plumber took a look at it swapped the IH for a new one, found the leak was still there, the pronounced that a new cylinder was required. The same thing happene last time the cylinder had to be replaced, 9 years ago (but a differen plumber !). The story that plumber spun me was that if the cylinde gets dented or stretched by over-tightening the IH, it forms a thi point in the copper wall that is vulnerable to pin-hole corrosion. Th latest cylinder did indeed have a dent near the boss, as if the I spanner had pressed against it during tightening.
Don't know if any of this makes sense, but I want to avoid the sam fate for cylinder number 3.
Thanks for all the other advice
-- 1tim23
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Wrote:

Get your self a high flow combi and be done with. No more space consuming cylinders to rot.
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1tim23 wrote:

I dont understand why youre going to the great trouble of replacing the cylinder when all it needs is soldering or gluing. They key in both cases is to get the hole spotlessly clean. Then either solder it, or use high temp epoxy available at car accessory places. With epoxy, use a good overlap for grip strength.
NT
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snipped-for-privacy@care2.com Wrote:

I tried polishing the dented area with wire wool and cleaning it revealing what looked like a pin hole, then soldering all over it (O how we laughed as the cylinder foam insulation caught fire, set off th smoke alarm etc etc). But there was still a leak coming from somewhere so I decided the best long term fix was to change the cylinder. It' quite hard to find every pin-hole when the whole cylinder is encased i foam. In a similar situation I might try your idea of epoxy. Though as you say, the key is to get everything really clean, which isn' always as easy as it sounds
-- 1tim23
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In an earlier contribution to this discussion,

I think others have already commented sufficiently on the basic plumbing bits, so I'll just comment on the control system aspects.
If you fit a zone valve in a gravity HW system, you'll end up with a C-Plan system (not S-Plan suggested in another post). A schematic and wiring diagram for this is shown in http://content.honeywell.com/uk/homes/systems.htm
This is quite cunning in the way in which the volt-free change-over switch in the zone valve is used to connect the boiler to the programmer when HW is required and to the pump (and CH circuit) when HW is satisfied. It is vital that you get the wiring of this correct.
The zone valve must be in a position where it doesn't block the vent path from the boiler to the F&E tank. The same would apply to the existing Cyltrol valve - so if you put the zone valve in the same place as that, you should be ok.
I'm not familiar with the EP3000 controller - but I suspect that it automatically runs the HW (and hence the boiler) when CH is selected. You need to stop it doing that, so as to have completely independent control over HW and CH. There may be a link which you have to remove to achieve this. If it *can't* be done, you'll need a new programmer.
Once you have independent control of CH and HW, it's well worth having independent timing as well. You can do this by using a programmable room stat, and using *that* to time the CH (with CH set to Constant on the EP3000). Set HW to Timed on the EP3000, and that will then just control the timing of ther HW.
--
Cheers,
Set Square
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