Adding UFH to Y-plan system

[mjl117]

Hi
I've had a single storey extension built with underfloor heating (about 35m2)
The plumber assured me that the UFH would have it's own "zone", but from my understanding of reading about Y-plan, S-plan etc this isn't the case based on the design of my system.

Previously I had a Y-plan (sealed) system which fed either the radiators or the hot water cylinder.

When the underfloor part was added a new 2-port valve was installed on the feed from the boiler as per the image below:

Do I need another 2-port value before the 3-port?

Or should it be converted to an S-plan? If so, does that 'just' mean adding 2x 2-port values for the radiators/cylinder in place of the 3-port valve?

I'm going to speak to the plumber, just rather have some basic knowledge before I do!

Thanks

 

[Madrab]

Not needed - the 2 port controls the UFH zone and that should be controlled by it's own thermostat(s)

The 3 port will be controlled by the HW cylinder stat and the radiator stat.

Y plan systems are now really considered to be obsolete and once the 3 port S-motors goes (theydon't last due to the way they work) then an S plan would certainly be a step in the right direction. Yes - 2x 2port valves, one on each leg to the CH/HW and a bit of re-wiring and the possibility of a bypass being needed.

I take it the blue arrow to X is pointing in the wrong direction? What is X anyhoo?

 

[mjl117]

Thanks, the X is a mixer (or last least what I assume to be a mixer)

I have two thermostats. A Nest to control the radiators and hot water. A Heatmiser to control the UFH.

The Nest is currently switched off (i.e. no demand) and I've just turned the Heatmiser up which is now demanding heat. This has resulted in the radiators coming on.

 

[Madrab]

The Nest is currently switched off (i.e. no demand) and I've just turned the Heatmiser up which is now demanding heat. This has resulted in the radiators coming on.

Ah ok, apologies, of course that's because the 3 port always has a port open.

To shut down the CH/HW side of things totally then yes just modify it to a an S plus so ideally you will have 3x2 ports by the end of it. No point in putting just one in and keeping the 3 port as it would just get overly complicated for no reason.

 

[picasso]

 

[Lee Edwards]

View attachment 358113

Thanks for this diagram Picasso. Can you explain how this is wired. Do I also need a 2 port for the ufh?

 

[ericmark]

The Nest is currently switched off (i.e. no demand) and I've just turned the Heatmiser up which is now demanding heat. This has resulted in the radiators coming on.

I don't like Nest as it does not connect to the TRV heads. However, the TRV head is in essence a motorised valve once an electronic head is fitted.

I have in some ways made a mistake myself, I have a C Plan with two motorised valves and two pumps, and it could have in hindsight have used a single pump and no motorised valves, and just allowed the TRV heads to control what rooms are heated and when.

I rushed into the work, without sitting back and working out what really needed to be done. My problem was someone clearly thought if they fitted two pumps, switching between them would select what was heated, in fact it just controlled which direction the water went.

Step one is work out what you want to happen. And what control you want? This is also impacted by the type of boiler used. My oil boiler does not care what temperature the return water is, only temperature it works on it that of water leaving the boiler, but I am using oil. With gas, often the return water temperature controls the modulation (turning down) of the boiler, and what you need to ensure is that no part of the system sends hot water back to the boiler causing it to turn down prematurely.

Motorised valves tend to be either open or closed, where a TRV can be part open, and last house I had a fan assisted radiator again not problem with a non modulating boiler, but with a modulating since it has no TRV, output controlled by fan speed, it can cause boiler to close down early.

The plumber

He should design the system. The three port valve defaults to DHW, and was used a lot in the past, as once power is removed the boiler can cool by heating the DHW, today often boiler have a built-in run on system, so no need for a default cooling path.

You are paying the plumber as an expert, use him. I didn't, and was left trying to work out how to wire the system up, in hindsight his idea of all programmable TRV heads and one pump would have been better.

Personally, I would not use UFH as it takes too long to respond.

 

[CountryFan]

Thanks for this diagram Picasso. Can you explain how this is wired. Do I also need a 2 port for the ufh?

Looking at the photo it is for the ufh. Maybe only have one thread going rather than hijacking two

 

[Lee Edwards]

Looking at the photo it is for the ufh. Maybe only have one thread going rather than hijacking two

Thanks for the advice.

I Believe this just closes/blocks the water from going to the hot water or heating circuit. I easily could be wrong

 

[CountryFan]

I Believe this just closes/blocks the water from going to the hot water or heating circuit. I easily could be wrong

Yes it does, but that's what you need I believe @picasso may know. If you look at it, the 2 port is for the ufh, the 3 port is then controlling the heating and or hot water as before. No idea why it's named a blocker valve

 

[Lee Edwards]

It blocks the water from going to the 3 port valve which is always open to one or the other so when the ufh is on the rads or the hot water would get hot without the valve blocking the way

 

[CountryFan]

It blocks the water from going to the 3 port valve which is always open to one or the other so when the ufh is on the rads or the hot water would get hot without the valve blocking the way

Oh of course, stupid me. So, the ufh is fed from one side, 2 port valve blocks to the cylinder/rads until they call for heat, thus opening the 2 port valve.

 

[Madrab]

Yes - it just allows a Y plan to be retrofitted and still keep all its components as they are. The 2 port would only need to be wired so when there was a call for rads or HW, then the 2 port would open, it wouldn't need to switch as the 3 port would already be doing that. Still easier to go to an S plan IMO as the 3 ports (Y Plan) are always a weak point in that system.

As suggested though, a new thread, linking back to this if reference is needed would be ideal.

(edit) just saw the other thread re this from picasso + dan, yes, the SL from the 3 port could be used to power the 2 port to open and then the orange out from the 2 port is the call for heat. The 2 port would also need a N and Earth and 240V connected to the grey to allow the orange in the 2 port to call back to the boiler. I think it might be easier with wiring to leave the 3 port to do what it's already doing and the 2 port is just powered to open, can't see why it wouldn't achieve the same thing.

 

[Exedon]

Or just get shut of Y plan valve (it will fail) and do S plan +.

 

[ericmark]

I Believe this just closes/blocks the water from going to the hot water or heating circuit. I easily could be wrong

Not that easy, unless using a non modulating boiler. I saw my son struggle, as he had not considered if any route left open, the return water will cause the boiler to modulate (turn down) on each branch, something needs to limit the water passing so the return is cool, until so many items have restricted the flow so the by-pass valve lifts.

I have looked at all underfloor heating, and no underfloor heating, but part underfloor heating will need some clever controls.

You are paying the plumber as an expert, use him.

As an electrician, I have found, these people who think they know it all, are specially annoying to those of us that do. I am sure it is the same with plumbing. I know when I was doing my degree, we joined other trades for some subjects, like maths, I have the lowest of the low of degrees, but it still took a lot of study, as an allied trade, I know how complex it is, and I employed experts in their field to do my central heating plumbing and also fitting solar panels, there is a point where you need to stand back and let them do their job.

Seen it so many times, where experts state, we gave him exactly what he asked for, but not what he wants.