diy ufh s,y plan conversion

7 Feb 2017
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United Kingdom
heres what ive got .

30 year old potterton netaheat

DIY ufh down stairs (not finished/connected)

30 year old potterton netaheat conventional boiler in kitchen downstairs

4 rads upstairs with thermostatic valves +heated towel rad with lockshields :)

cylinder ,pump and 3port valve in airing cupboard with wiring box .

system has no room stat anywhere . just on the cylinder .

So im thinking i need to make it S plan for independent control of each , chop out the 3 port valve to start with .
put in 3 two port valves (on the right pipes)
one for the cylinder one for rads and one for ufh

sounds easy... i think .
Will that work if im only using upstairs rads or ufh ?
how would the final temperature be controlled/limited if the hot water cylinder stat never gets hot?
can the boiler limit itself....i think not?

also do i need some kind of auto bypass somewhere ?

any help appreciated .
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Will that work if im only using upstairs rads or ufh ?
With individual valves, each zone is independent so can be operated on it's own or in any combination with the others.

how would the final temperature be controlled/limited if the hot water cylinder stat never gets hot?
Not sure what you mean by the 'hot water cylinder stat never gets hot' - the boiler heats water to something like 70C, this is used to heat the hot water cylinder.
If the radiators require heat, that 70C water will be circulated through them.
The UFH will have it's own blending valve and circulator so that the floor temperature is significantly lower.
All of which will be controlled by the various thermostats - one for the cylinder, at least one for the room(s) where the radiators are and another for the rooms with the UFH.
With the changes you are suggesting, all of the controls will need to be completely replaced anyway.

can the boiler limit itself....i think not?
Boiler will contain a thermostat to regulate the temperature it heats the water to, but that is unrelated to the other controls.

also do i need some kind of auto bypass somewhere ?
Yes, the existing bypass is most likely the towel radiator. With Y plan, at least one of the ports is always open. With S plan, they can all be closed so a bypass is required.
You will also need to make changes to the wiring. The control philosophy of the 'Y Plan' system and the 'S Plan' system is somewhat different.
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thanks for taking the time to reply

Flameport: I probably(definitely) don't fully understand all whats involved....

I thought the cylinder stat served to limit the heat of water in the tank and rads (as it can only do hot water only or HW and heating) either way the tank stat would stop it all from getting too hot .
If the water only went to the rads what would stop the boiler ???
My new heating controll system and room stats would :)

I think I've got a better idea now, thanks .

I will have to get some new controls for the new 2 port valves and ufh actuators anyway so ill need to have in mind that it will need to accommodate 3 room stats up stairs and 1 down stairs (open plan) also somthing to switch HW and to run 2 pumps when req.

Stem: I though the only wiring i would keep is in between the wiring box (by tank upstairs) and the boiler and programmer (downstairs) the only new wiring would be the ufh pump and actuators going to a controll box ...thinking about it perhaps it would be easier just to start again .

anyway I will want something modern like ...nest heatmiser honeywell wireless . I have looked a bit but I'm unsure .
I have got an amazon echo so it would be nice to use that with heating control's.
I do know I aint putting a bloody nests all over the place ..they're £200 each!!! and they seem to want to take control rather than be controlled .

IF you have any advise on that side of things I would love to hear it .

I will get one of these

and one of these if thats the right thing ...

Where would my new bypass go ? and where should the bypassed hot water end up ?
I assume it goes on the hot pipe coming to the old 3 port valve as the first thing the hot water encounters before it can reach any new valves that may be closed ?
and joining it to the nearest return anywhere ? or should i vent it into the toilet cistern so i can have a hot flush sometimes .

thanks again for the help .
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