Posted by: @davesoa

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But what with or do I even need one? Could the UFH be set up so it runs automatically when the heat pump does

You dont need one and you dont want one as it conflicts with the heat pumps own controller.

What does the thermostat actually control/connect to, have you got a buffer between heat pump and UFH, and if so how many ports?  Have you got a secondary water pump?  With that info it should be possible to work out how to disable it.

@jamespa The Honeywell connects to the UFH pump and the wiring then triggers the heat pump when the desired temperature is required. As it did when we had the gas boiler. There was a Nest thermostat controlling the radiators and water heating. 
i have no idea how many ports anything has - i keep well away from electrics. 
There is buffer in the system but I don't know the answer to your question. 
From your questions it sounds possible - I think I’ll need a very competent plumber.

Posted by: @davesoa

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@jamespa The Honeywell connects to the UFH pump and the wiring then triggers the heat pump when the desired temperature is required. As it did when we had the gas boiler. There was a Nest thermostat controlling the radiators and water heating. 
i have no idea how many ports anything has - i keep well away from electrics. 
There is buffer in the system but I don't know the answer to your question. 
From your questions it sounds possible - I think I’ll need a very competent plumber.

You need a plan first I think, it's really about wiring not plumbing and personally wouldn't trust anyone to get it right without a plan.  

Really this should have been sorted out when the heat pump was fitted, a quick scan of the manual suggests that the Ideal heat pump controller is quite capable of controlling the whole system, which is always best and simpler.  However you are not alone that it wasn't.  Is it possible you could get the installer back to finish the job?  It really needs someone familiar with the Ideal controls.  That said he would probably just replace the thermostat because it's the lazy thing to do.  You may end up doing that anyway because sorting it out properly requires thinking, not just following instructions, and you might not be able to find anyone who can think!

The answers to the following questions might help determine the best and most practical option (which may not be the same!)

• How is the water controlled now and is your heat pump the R32 or the R290 model?
• Is the nest thermostat still there (you say 'was') and if so what is it doing?
• Does the control system as is work to your satisfaction?

OK I've thought some more about this.  I think you have, in reality, two options:

1. Replace the failed thermostat like for like or

2. Rewire the whole thing properly as it should have been wired in the first place, so that the Ideal controller is controlling everything.

The latter needs someone who is intelligent and ideally familiar with Ideal controls, although intelligence enough will suffice if they are diligent and can read.  

If you want to do (2), which undoubtedly is the better option (and should, IMHO, have been done when the heat pump was fitted), your challenge is to find someone who won't mess it up.  Your best bet may be to contact Ideal, describe the job, and ask for recommendations.  If I am brutally honest the only person I would trust to do this job in my house 'on the fly' is me (I'm not offering).  Alternatively someone who produces a circuit diagram in advance which you can check eg against the Ideal manual should be safe.  I wouldn't trust someone to turn up and just 'get going' without first producing a wiring diagram. 

I hope that helps, do post back with any further questions, which way you go, and your experience

Whether you need a separate thermostat for your UFH heating depends on 2 things, what flooring you have and what the maximum temperature is that the heat pump might supply.

I believe the max floor temperature should be less than 40C to not burn feet, especially bare children’s feet. But your system might have been designed to go higher, 45/50C. Do you know what the max temperature is?

We chose vinyl tiles to go over our ufh and the cement that attaches them must see no more than 29C. Our utility room has a simple down mixer so it is always set to about 26C and the old thermostat is disabled. In an ideal world it would be weather compensation by the ashp, but instead it is simpler still, as it get warmer or cooler I alter it a couple of degrees.

We carefully compared the water pipe temperature as goes under the concrete fill and the floor surface and they were within 1C. Don’t get fobbed off with ‘the surface is always much less than the water.’

I concur with James you need a smart electrician who understands ashp controls (or is prepared to learn).

@judith We have an oak engineered wood floor laid over 20 years ago and was designed to run at a max of 50C. It has been very effective over the years.

@jamespa -

1. The HP is an 290.

2. The Nest was replaced by the Halo Lite.

3. The controls, as they are now, work - in that the radiators get warm and the UFH pump is triggered by the Honeywell (which hasn't failed but is just very clunky to use) and water flows to the UFH. It hasn't been cold enough yet to test the effectiveness of the floor since the change over. I think the installers did what they contracted to do in that I have a working heat pump and UFH also heats up. Now I've started using the system it does appear there may be a much more effective way to do this without a second thermostat as @judith describes.

4. Your suggestion to contact Ideal is a very good one and I will do that and post back with their reply.

Thanks

Posted by: @davesoa

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3. The controls, as they are now, work - in that the radiators get warm and the UFH pump is triggered by the Honeywell (which hasn't failed but is just very clunky to use) and water flows to the UFH. It hasn't been cold enough yet to test the effectiveness of the floor since the change over. I think the installers did what they contracted to do in that I have a working heat pump and UFH also heats up. Now I've started using the system it does appear there may be a much more effective way to do this without a second thermostat as @judith describes.

 

OK, so just to clarify the radiators and the heat pump are controlled by the Halo Lite; the UFH pump is controlled by the Honeywell, and they are both set to same times and temperature.  Is this correct?

Is the water for the UFH mixed down or are the radiators running at same temp as UFH?

Your first point.

Yes that’s correct  

Second point

The water for the UFH is/was mixed down but there is a TRV now fully open so the water will be the same as the radiators (the flow temperature is set at 50C). 

Posted by: @davesoa

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The water for the UFH is/was mixed down but there is a TRV now fully open so the water will be the same as the radiators (the flow temperature is set at 50C). 

OK.   Thats really helpful

Presumably therefore the UFH pump frequently switches off, because the water temp (not mixed down) is higher than is needed to keep the UFH 'zone' at temp.  Or does this part of the house tend to overheat/oscillate?  

A key question, in terms of rewiring, is: is it possible to operate the rads and UFH continually at the same flow temperature, ie as a single zone (or possibly with mixing down for the UFH).  This would be ideal if its possible, but it may not be depending on how the rads (and indeed UFH, although that is less critical) were sized.  

Do you happen to know the design flow temp is for the rads, and are you operating weather compensation or a fixed flow temp of 50C?  Have you run this through the winter yet or was it installed this summer?

@jamespa Good questions.
The HP was installed in May so I have no data yet on the UFH performance- it’s been so warm (and the house is well insulated) that I haven’t been able to assess heating performance. Everything is working (as in pumps work, water circulates, the UFH pump circulates) and hot water is produced (COP of 3.88 over the summer). 

The UFH has the same flow temperature as the HP. Weather compensation is on but the Ideal control box doesn’t give any real opportunity to fiddle. Essentially I was told ‘just let it do its thing’ so I will. 

Posted by: @davesoa

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@jamespa Good questions.
The HP was installed in May so I have no data yet on the UFH performance- it’s been so warm (and the house is well insulated) that I haven’t been able to assess heating performance. Everything is working (as in pumps work, water circulates, the UFH pump circulates) and hot water is produced (COP of 3.88 over the summer). 

The UFH has the same flow temperature as the HP. Weather compensation is on but the Ideal control box doesn’t give any real opportunity to fiddle. Essentially I was told ‘just let it do its thing’ so I will. 

OK.  It may be best to run it through the winter as is and collect observations, using the intervening time to find someone to do the job (as nothing is broken you have the time!).

Without a plumbing diagram and some information on the design temperatures for the rad circuit and the UFH its going to be difficult/impossible to design a better control strategy.  Someone coming in should be able to work out the plumbing diagram (although if your installer left one it would help!), the observations on operation will help.  Ideally the buffer would come out to reduce complexity and improve efficiency, but that may be a step too far for you.

I think the principal control options (in decreasing order of simplicity/efficiency) are:

1. Operate rads and UFH at same WC-controlled temp, balancing the flows to get the house temp right.  Everything controlled by the ideal controller.  Essentially this is operating as a single, WC controlled, zone, which is generally best if possible.

2. Operate rads on WC and UFH on a fixed mixed-down temp.  Everything controlled directly by the ideal controller

3. As (2) but UFH pump additionally controlled by a simple thermostat (no time program) via the ideal controller

4. Operate on WC but have a thermostat 'overlay' in both 'zones (rad zone and UFH zone), all pumps and thermostats connected via the Ideal controller

Glancing at the ideal installation manual I think (3) and (4) might require a '2-zone kit' (whatever that is).

The Ideal manual has diagrams for several of these

The water pump arrangements may need tweaking as well as the wiring, so it definitely needs some thought and planning, not just going in with a screwdriver and spanner. 

PS there is plenty of opportunity to fiddle with parameters.  You probably need to go into the installer menu to do so though and, until you have a plan for going forward, its probably best not to.  If you haven't already, I suggest you may wish to download the installation and maintenance instructions which tell you more about its capabilities.  It seems to have plenty of control features, as ever the challenge is (a) working out what some of them actually do and (b) working out how to apply them to your house.  Plenty of installers dont achieve (a) much less (b) so far as I have been able to tell from my limited first hand experience and what is reported here.

PPS  I think it might be possible to simulate (more or less) most if not all of the above control strategies with your existing setup, another reason to ride the winter out before making a decision.  It really would be worth your while sketching out both the plumbing and the control, even if its not perfectly right it will prompt the questions for you and someone coming to fix it (and anyone on this forum) to ask.