Weird Heating System - How Do I Change To S Plan

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It appears that my brother has bought a bungalow with an unconventional heating system, that doesn't fall into any category (eg. Y, C, S plan)

Its like a C plan, but the single 2 port valve is on the heating flow. The HW has no control valve, so whenever the heating is on, the primaries on the cylinder are also being pumped from the boiler too.

He wants to replace the ancient boiler. Can we convert to S plan, by adding a 2 port valve to the cylinder primaries? Obviously the wiring would need to change too, but what other changes are necessary?
 
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Can we convert to S plan, by adding a 2 port valve to the cylinder primaries? Obviously the wiring would need to change too, but what other changes are necessary?

Thats all you need to do add the valve repipe to the cylinder add a bypass and wire the thing up. might be worth while getting a full s plan kit. And if your changing the boiler i think that you might be putting it onto a pressurised system. so a pressure test of the system should be done.

Nath
 
Agreed, apart from the pressure bit. Is it open - vented at the moment? ie header tank in the loft? A bit of prep work would be advisable. How do the rads perform at the moment? What's the state of the water in the tank? Could you introduce a couple of litres of gentle system cleaner for a couple of weeks?
I would take the opportunity to get a full lifestyle pack, 22mm bypass (auto) and new pump with quality valves maybe. and new rad valves which can be easily swapped.
Once drained down the existing zone valve should be swapped for new, tee in/pipe up hot water valve and bypass and upgrade wiring to new programmer with cylinder stat in series with new valve.
 
Thanks for the advice.

He wants to keep it vented, and change as little as possible as it works really well.

2 more questions.

1) Where would the bypass go? Between the primaries on the cylinder (obviously before the new motorised valve, which would be on the cylinder primary flow)?

2) Would it be within regs to leave the system as it is, but just replace the boiler?
 
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Below is a sketch of the system, with the addition of the new 2 port valve for HW. Would this be the correct position?

Also shown is the position where I think the bypass should go. Is this correct?

If we were to have just the boiler replaced, without the other changes, would this be within the regs?

(N.B. the feed and vent pipes aren't shown, but are above the boiler.)

 

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