WC + independant zone valve

[Mr Blobby]

So this month is heat pump month, and I am seriously excited about it.  The challenge will be, however, to convince our builder and plumber not to hand over total control of the ASHP install to a third party installer.  Thanks to the useful guidance on this forum and the low heat demand in our house, I am keen to run WC mode without any buffer tank or additional pumps if possible.  I suspect the third party installer would prefer a more expensive, less efficient design.  I will soon find out.

 

We have two UFH manifolds, GF and FF.  It would be nice to treat the FF manifold as a seperate zone.  The GF zone will always be open and should have enough volume to satisfy the flow requirement of the pump. 

 

The panasonic text book provides a direct (no buffer) 2-zone implementation but requires flow temp sensors on both zones and valves on each zone, all connected back to an additinal circuit board in the ASHP.  I'm not convinced it needs to be that complicated and chat gpt concurs.

 

I think there is a far simpler solution, to configure the system as a single zone, bog standard WC implementation, but then install a two port valve before the FF manifold connected directly to a thermostat on the first floor.  This would provide a way of isolating the zone altogether.  The heat pump would not need to know about this seperate zone.  A thermostat with cooling function seems to be available that would cool down to cooling setpoint so, when the heatpump is set to cooling mode, then the FF thermostat would also be able to open the zone valve to the FF if the FF is overheating.

 

The simplicity and low cost of this design appeals greatly.  No additional flow temp sensors, one zone valve, no additional circuit board.  What's not to like?

 

Is this standard stuff, do others on this forum control zones like this, perhaps to switch fancoils in/out, with an indepentant thermostat/relay/valvethat is wholly independant of the ASHP?  Or is is bonkers?

 

 

(The more complicated, integrated panasonic implementation is in the attached pdf)

 

 

 Direct two zone third party controls 5kW 7kW 9kW.pdf

Edited May 19 by Mr Blobby

[JohnMo]

We used an external permissive to start stop the ASHP. So similar to what you propose.

 

For me knowing what's going on is important, so I have used a wiring centre for the UFH, this is equipped with room sensors, not thermostats. The signal from the wiring centre goes directly to ASHP, not to UFH actuators etc. The whole system can also be moved between heat and cool via a volt free signal. So open circuit is heating mode closed is cooling mode. ASHP using the same signal, so use a single switch to move both the UFH wiring centre and ASHP between the two modes.

 

We have in effect two heated areas the house and summer house. After quite a bit of experimentation figured I could run as a single zone and either the summer house or the house could call for heat, and both got heated together. The house floor acting as a buffer. Running for an hour or so to heat up the summer house has zero effect the house.

 

Have run pure WC and if you can do that, I would, but we have found using the wiring centre and it's sensors, giving the heat pump permission to run, meant we ran better and could keep away from min modulation longer and regularly get CoP of 5+.

 

I would try to run as a single zone, decrease the upstairs output with reduced loop flow where needed. You are going to running very low temps, our curve starts at 26 degs at 10 Deg oat and goes to a massive 28 at -5 degs. So likely hood of overheating is zero.

 

I would make sure price wise you are not being screwed over

7 hours ago, Mr Blobby said:

builder and plumber not to hand over total control of the ASHP install to a third party installer. 

So MCS uplift and plenty with a profit to make

[Mr Blobby]

2 hours ago, JohnMo said:

I have used a wiring centre for the UFH

 

I had hoped to not have a wiring centre, but as you can tell I don't really know what I'm doing 😕

 

 

2 hours ago, JohnMo said:

 

I would make sure price wise you are not being screwed over

 

Exactly this. 

The heat pump costs £2,599 ex VAT.  How much can they charge to install this?    My guess is minimum 6k for a days work.  Maybe more.  Maybe I'm being too cynical. 

 

Although I've told the plumber I want WC and no buffer so we may never hear back from the installer 😂

 

2 hours ago, JohnMo said:

So MCS uplift and plenty with a profit to make

 

I'll update here after I get the quote....

 

Edited May 19 by Mr Blobby

[JohnMo]

11 minutes ago, Mr Blobby said:

had hoped to not have a wiring centre, but as you can tell I don't really know what I'm doing 

Just choose a wireless thermostat that switches between cool and heat easily - I say wireless then you can move it to where it gives the best representative house temperature. But the Panasonic controller has one built-in (pretty sure), just use this. It should do cool and heat out the box.

[Nickfromwales]

59 minutes ago, Mr Blobby said:

My guess is minimum 6k for a days work.  Maybe more.

I’m on my way.
 

I can do it for £5999, on mates rates.

 

Can’t you just find a decent local plumber (“heating engineer……”) to put pipes from A-B with you supplying?

 

It’s ridiculously simple work, easier than putting a combi boiler in.

[Indy]

15 hours ago, Nickfromwales said:

I’m on my way.
 

I can do it for £5999, on mates rates.

 

Can’t you just find a decent local plumber (“heating engineer……”) to put pipes from A-B with you supplying?

 

It’s ridiculously simple work, easier than putting a combi boiler in.

This is so often touted and I really don't know where people are finding these people that will connect pipes from A-B without asking too many questions?!

 

Every single company/plumber I've contacted independently has refused to do anything of the sort. They will supply all the parts and do the install and are usually charging above £500/day for labour - without which the usual get out clause is that we can't provide warranty of any of the work otherwise. Even if I was to accept that, they then stop responding when asked to provide a labour only quote.

 

I'm sure there are people out there that can do this - I just haven't found them in ~ 2years of searching on and off. To the point, where I just went with the builders default option as life is too short and I have better things to do with my time!

 

Edited May 20 by Indy

[Mr Blobby]

18 hours ago, Nickfromwales said:

Can’t you just find a decent local plumber (“heating engineer……”) to put pipes from A-B with you supplying?

 

It’s ridiculously simple work, easier than putting a combi boiler in.

 

My thoughts exactly.  We have a cooperative plumber who did all the first fix stuff who can join the pipes and stuff.  But he wants to get his "installer" mate to supply and fit the heat pump.

 

Builder is super keen to get the heat pump installed to get the floor temps up before tiling. I have sent him a link to buy the heat pump with a 12 day lead time, but he insists on waiting for plumbers mate to quote for supply and fit.

We still haven't heard anything back from instalelr, but I think he is on holiday this week.  Or he just isnt interested because I want some input into the design.

[Nickfromwales]

3 hours ago, Mr Blobby said:

 

My thoughts exactly.  We have a cooperative plumber who did all the first fix stuff who can join the pipes and stuff.  But he wants to get his "installer" mate to supply and fit the heat pump.

 

Builder is super keen to get the heat pump installed to get the floor temps up before tiling. I have sent him a link to buy the heat pump with a 12 day lead time, but he insists on waiting for plumbers mate to quote for supply and fit.

We still haven't heard anything back from instalelr, but I think he is on holiday this week.  Or he just isnt interested because I want some input into the design.

Time to put your foot down then?

[dpmiller]

or get on the tools yerself. 

[JohnMo]

Assuming time of use tariff 

 

Direct UVC immersion cylinder - size to suit house bedrooms and storage temp.

 

ASHP, anti freeze and isolate directly on ASHP, pipe through wall flow - direct to UFH manifold isolation valve return, filter and strainer to Panasonic spec, through wall to ASHP isolation valve.

 

That is all the plumbing done. Run in 28mm Hep2O. No Flexi pipes needed. Insulate piping

[Dillsue]

16 hours ago, Mr Blobby said:

Builder is super keen to get the heat pump installed to get the floor temps up before tiling. I have sent him a link to buy the heat pump with a 12 day lead time, but he insists on waiting for plumbers mate to quote for supply and fit.

We still haven't heard anything back from instalelr, but I think he is on holiday this week.  Or he just isnt interested because I want some input into the design.

So you need to decide who's taking on responsibility for the systems performance and providing the warranty for that. If you want things done your way then make it clear that you take responsibility. If you want someone to blame if things don't work then you probably need to leave the design and install to the builder/plumber/HP guy.

 

As mentioned above its straight forward to install a HP........if you understand what needs to be done!!

[Mr Blobby]

1 hour ago, JohnMo said:

Assuming time of use tariff 

 

Direct UVC immersion cylinder - size to suit house bedrooms and storage temp.

 

ASHP, anti freeze and isolate directly on ASHP, pipe through wall flow - direct to UFH manifold isolation valve return, filter and strainer to Panasonic spec, through wall to ASHP isolation valve.

 

That is all the plumbing done. Run in 28mm Hep2O. No Flexi pipes needed. Insulate piping

 

We have a decent plumber to do all the pipework, which I suspect is largely the same as he would normally do with an oil boiler, so I don't really need to do very much.  At this stage the UVC (300L is biggest we can fit in undesized plant room) isn't even going in yet, this is just to get the heating on to get floor temps up before tiling. 

All I need to do is connect the electrics and the controller cables to the circuit board.  In our simple configuration this looks breathtakingly simple.  Frustrating as this is, I need to play the game and wait for the installer to come back with an unacceptable proposal before I can make a counter proposal.

 

53 minutes ago, Dillsue said:

If you want things done your way then make it clear that you take responsibility.

 

Heat pumps are rare here, builder and plumber see them as some mystical box that demand expert knowledge and they want an expert installer to hand this over to.  I would be happy to take responsibility but theres a bit of a diplomacy dance to do first 🙄

 

53 minutes ago, Dillsue said:

As mentioned above its straight forward to install a HP........if you understand what needs to be done!!

 

I've read the manuals and and watched the you tube videos. What could possible go wrong? 😆

Edited May 21 by Mr Blobby

[Dillsue]

8 minutes ago, Mr Blobby said:

Heat pumps are rare here, builder and plumber see them as some mystical box that demand expert knowledge and they want an expert installer to hand this over to.  I would be happy to take responsibility but theres a bit of a diplomacy dance to do first 🙄

 

I've read the manuals and and watched the you tube videos. What could possible go wrong? 😆

Next to nothing to go wrong if you've done your homework.

 

I guess if your builder is responsible for building regs compliance and sign off then he may be a bit hesitant to hand responsibility to you but if you make it clear he's not responsible for the heating system performance it's hard to see why he'd be concerned. If you put it writing it's a valid change to any contract you have. If he's got a mark up on the heating system then he's potentially a bit out of pocket if the HP installer is out of the picture.

[SimonD]

On 19/05/2026 at 11:30, Mr Blobby said:

The GF zone will always be open and should have enough volume to satisfy the flow requirement of the pump. 

It's not really about having the volume to satisfy flow requirements. The volume is to take the heat input from the heat pump and deliver it where it's needed. That's the beginning of working out your volume requirements. From a design perspective this is the start. 

 

On 19/05/2026 at 11:30, Mr Blobby said:

The panasonic text book provides a direct (no buffer) 2-zone implementation but requires flow temp sensors on both zones and valves on each zone, all connected back to an additinal circuit board in the ASHP.  I'm not convinced it needs to be that complicated and chat gpt concurs.

 

I think there is a far simpler solution, to configure the system as a single zone, bog standard WC implementation, but then install a two port valve before the FF manifold connected directly to a thermostat on the first floor.  This would provide a way of isolating the zone altogether.  The heat pump would not need to know about this seperate zone.  A thermostat with cooling function seems to be available that would cool down to cooling setpoint so, when the heatpump is set to cooling mode, then the FF thermostat would also be able to open the zone valve to the FF if the FF is overheating.

Glad to hear chat gpt agrees on your design. The addition of a pipe temp sensor and valve with a pcb isn't really complicated at all because you've got to run all the cabling back to the Panasonic unit you've selected. By the time you've wired up another stat, zone valve, and a wiring centre, you might as well have just integrated it into the heat pump unit itself. This gives you more flexibility should you experience a control problem once it's up and running.

Once you separate controls away from the heat pump, you're actually adding complexity plus additional control demands on you. You're potentially causing an additional rod for your own back.

If the system design has been done correctly. I'm assuming someone sensible has done this and actually designed to ufh loops to room heat loads as opposed to provide a standard geometric exercise trying to fit pipes into the space to 150mm spacing, then simply running the whole system open on weather comp should be all you need.

TBH, my alarm bells are ringing as you wouldn't believe the rubbish I see that's a result of a customer getting their builder and plumber to put in the UFH and then ask another person to install the heat pump. Usually they haven't got a clue on the UFH design or they farm it out to a UFH company that apply no sense to matching the design to the room demand.

 

This is where you need to go back to before trying to figure out your control strategy. Are you having to put this in due to poor system sizing design in the first place? If so, then go with the manufacturer options because then you can move away from relay control to electronic mixers with separate curves to balance the heat across the manifolds if you need to, ideally controlled from the heat pump.

[Mr Blobby]

On 21/05/2026 at 15:09, SimonD said:

The addition of a pipe temp sensor and valve with a pcb isn't really complicated at all because you've got to run all the cabling back to the Panasonic unit you've selected. By the time you've wired up another stat, zone valve, and a wiring centre, you might as well have just integrated it into the heat pump unit itself. This gives you more flexibility should you experience a control problem once it's up and running.

 

You make a good point here about wiring two zones back to the heat pump.  It just seems unecessary to have a zone-1 valve and sensor at all, because the GF zone 1 valve will always be open so the zone valve is effectively redundant.  We will never be running the FF heat without GF heat, but this is of course how Panasonic controllers expect normal people to run their heating with these options.

 

On 21/05/2026 at 15:09, SimonD said:

Once you separate controls away from the heat pump, you're actually adding complexity plus additional control demands on you. You're potentially causing an additional rod for your own back.

 

The plan is for the first floor zone to be off most of the time, except maybe for cooling in wetaher like this, but I take your point.  This is just an idea at this stage to have an open zone and an independant second zone. I had hoped that this was something more common that would be commented on here 😕

 

On 21/05/2026 at 15:09, SimonD said:

If the system design has been done correctly. I'm assuming someone sensible has done this and actually designed to ufh loops to room heat loads

 

I have a spreadsheet that I put together ages ago, so a person not very sensible at all is responsible for the loops.  I have completely forgotten how I arrived at the formulae and numbers but, in theory, we have about 11 W/M2 heat demand per room, and with 200 centres GF and 250 FF that should return 22C GF 20C FF with about 27/22 flow and return.  Or something like that.  It will be interesting to see if theory and practice are the same 🤔

 

On 21/05/2026 at 15:09, SimonD said:

you can move away from relay control to electronic mixers

 

I'm hopeful that the FF zone will not be used very often for heating and, if so, then mixed circuits are probably unecessary.  In theory anyway. 

In theory the FF loops are primarily for cooling but with insulated screed underneath and engineered  timber on top it may be that only the FF bathrooms with tiled floors get the cooling effect 😬

 

[Mr Blobby]

Just spoke to the installer/supplier on the phone.

He spent 10 minutes trying to convince me I needed actuators on the manifold, a buffer tank and a hitachi heat pump instead of Panasonic.  And AC as well because passive houses always overheat.

 

He's putting together a price list for all the Panasonic bits sans buffer. 

Edited 4 hours ago by Mr Blobby

[JohnMo]

If you set as 2x zones. One zone valve for upstairs controlled via a single simple thermostat. But not sure I would bother.

 

Or accept the UFH upstairs output is low anyway with the more open centres on the pipes, just let it run with downstairs as a single zone, and accept the extra water capacity as insurance against short cycling. This would ultimately allow a lower flow temperature overall and better CoP.

 

But you may find you minimum realistic flow temp in mild weather is actually warmer than you really need, in this case use the controller thermostat in a suitable location to act as heating permissions. In mild weather 7 to 10 degs, you find the heat pump only runs a few hours a day.

 

So, one zone, use the main controller thermostat and almost flat WC curve.

[JohnMo]

8 minutes ago, Mr Blobby said:

actuators on the manifold, a buffer tank and a hitachi heat pump instead of Panasonic.  And AC as well because passive houses always overheat.

Actuators - no need, then you don't need a buffer.

Hitachi, are quite good, but you need additional widgets for cooling

AC just do UFH cooling.

 

Maybe find a new installer

Edited 4 hours ago by JohnMo

[Mr Blobby]

5 minutes ago, JohnMo said:

Or accept the UFH upstairs output is low anyway with the more open centres on the pipes, just let it run with downstairs as a single zone

 

I like the simplicity of this very much, and you are probably right that it would work given the lower heat FF output at wider centres (and timber covering).  

 

We had originally planned to install only GF loops, the FF loops were later added because of an increase in expected solar gain because we were unable to install planned external blinds on some windows.  I think I may be stuck in a mindset that there should be some control to switch off the flow to FF loops just because they were originall excluded.  Maybe not  🤔

 

 

18 minutes ago, JohnMo said:

Actuators - no need

Hitachi, are quite good, but you need additional widgets for cooling

AC just do UFH cooling.

 

I agree 👍. 

 

[JohnMo]

We did at one point very tightly control house temperature and it varied maybe 0.5 Deg. But depending on outside temp etc the way the house temperature actually felt changed, so sometimes you felt warm others cool (I'll put my jumper on).

 

We have relaxed (simplified )that control and just use a room sensor to control everything, our WC curve is 26 to 28 degs, so almost flat. Thick screed (we have) is pretty slow to heat and cool down again. So what happens in our house, in heating season, the UFH generally ends up running at night and spends all day off, down to about freezing and then the heat pump runs for some time during the day also. Colder it gets the longer the run time. Room sensor thermostat set to same temperature 24/7 for heating with a 0.3 hysterisis.

 

We get some undershoot while floor plays catch-up, but we are in bed then so that's fine.