JohnMo

Really you should consider keeping it simple. UFH doesn't need complex control system or smart anything. Simple wiring centre, have each floor as a zone, or even the whole lot as a single zone. The more you split the system in to small parts the more likely the heat source will short cycle and burn through energy.

Think the flow switch is in a failed condition, so read a huge flow rate. This allows the heat pump to run for a while until the controller logic says, that cannot be correct, let's shutdown. First check the wires for the flow meter meter, disconnect then reconnect the wires first. If that fails the switch may be goosed. However if under warranty call the installer, that's what the warranty is for.

You could try to balance the system, set weather compensation and dump all but one thermostat and use the whole system as a single zone? Big volume of water available to heat pump, long run times, lower flow temps (than on/off times), win - win

Good luck, trouble with ufh is the reaction time, mine is quite extreme at 6 to 8 hours for a change to be seen. So no point relying on thermostats or anything smart. Been there tried and failed. My night setback starts at 4pm and ends at 1am. My thermostats fitted cost £5, they basically do nothing (being set above the room temp), could remove tomorrow and it would make little or no difference to the heating. Read Jeremy Harris's threads on home automation and trying for a couple of years to get really smart with ufh control. In the end it was all dumped and a simple +/- 0.1 hysteresis thermostat installed. On my boiler there are three setting that affect modulation, temperature setpoint, max temperature setpoint and gradient. The delta T is a moving target, the hotter the flow temp the wider the delta T, this defined by the boiler controller. A 30 deg flow temp will have a 26 degree return temp, as delta T decreases, supply temp is increased, this will increase until return temp is equal to set point or max temperature set point is reached which ever comes first. The gradient limits how quickly the temperature ramps up (range of 0-15). Set to O and the gradient is removed, so boiler ramps direct to set point as fast as possible, at low temps boiler trips a few seconds later, this is great for 80 deg flow temps. Gradient 1 it applies 1 degree per min max, this can cause return temp and delta T to go out limits. Mine is set to 2 and it lets the boiler run for about 10 to 15 minutes. At a gradient of 4 the boiler stops after about 3 to 4 minutes, not great. I think most boilers have a gradient that can be changed, but the setting is well hidden. Nothing is written in my installer manual, except a small reference to it, many hours of searching later, I found out what is was and how to change it.

I think implementing DHW cylinder weather compensation is somewhat over thinking things and may not be easy to implement and give little or no benefit. If you haven't purchased your DHW cylinder, purchase one suitable for a heat pump with a 3m2 coil, then you can heat it at much lower temps and get a very low return temp. Trying to heat via a normal coil at low temps gives a small DT and isn't efficient. If you are doing weather comp on the heating, why do you need external control system, your boiler has all this built in, add the external sensor and the Apha diverter valve - job done. Simple over heat thermostats are all that's needed, set a couple of degrees over ideal room temp, balance system to get ideal room temps. Set your WC curve, balance your loops and the system then looks after itself. Adding third party equipment just makes a simple system, expensive and messes with things in an unhelpful way. Efficiency is likely to be low as a result. Based on loads of testing on my system, heating the buffer on a thermostat, will yield an efficiency (gas to UFH heat at the manifold) of around 95%. Leaving the buffer to float on boiler flow/return temps will give somewhere close to 105 to 110%, due to lower flow temps. My previous complicated system (before simplification and efficiency improvements) used 30 to 50% more gas, depending on the weather. My last 30 hours of operation (average outside temp -1) gave a system efficiency of 113%.

It's not set for weather compensation is it? Seen it plenty of time on here recently, where the weather compensation curve has been set the wrong way around, so as it gets colder outside the flow temp also gets colder. Have you checked?

Not got the same boiler, but have found on mine, the following. On the controller there is a user menu and an installer menu. In the installer menu under the info tab, can see what the set point is for the boiler. Ours is running WC, and when I looked last the set point was 30. The heating pump runs all the time in WC, when the return temp has dropped a couple of degrees below set point, the boiler fires up. On mine I can set what is called the gradient, this is how quickly the boiler gets up to temp, I have set this as low as I can, so the boiler run time is high. Once the boiler has got to the set point temperature on the return water or if the max supply temp has been reached the boiler switches off. My max is set to 40, so boiler either goes to 40 or a return temp of 30 which ever occurs first.

I have two Titon units, but found the same units are sold and rebranded by Beam for lower prices. Also found the technical response from Titon was great, when I asked for technical assistance. The unit I bought from eBay for super cheap prices, had a failed motor speed sensor, parts to fix where with me the next day. Can't fault that.

I am taking the meter reading, popping it in to OVO (my gas supplier) app, this give me an exact metered and calorific value converted kWh consumption since last meter read. I have an energy meter at the UFH, it measures, flow rate and supply and return temps and gives instantaneous kW heat rate and the accumulated kWh. This seems to be most accurate way I could think of and heat losses are included in the total. Divide gas consumption by energy meter read over the period and multiply by 100. Ideally this will be over a period where no DHW is being used, as I have the UFH on 24/7 as a single zone, overnight is best. Or do it over a few days and take my typical 5kWh off for DHW. On a really cold day and low DHW day, even without adjusting for DHW the energy meter is reading the same or lower than gas consumption.

There are three different devices. Volumiser goes in either the supply or return piping, it just adds volume. It is a simple in/out devise, it does not provide any hydraulic sepereration. Buffer as above by @PhilT. Can be 2, 3 or 4 port, but separates the primary and secondary circuits, and is connected to both the flow and return circuits. Simpler to a LLH but with additional volume.

Very true, with a large HP, but in the context of a small exhaust air HP, the OP was discussing, which should only draw 100s of W, maybe not.

People will often tell you a buffer or volumiser kills efficiency, if well insulated and operated without a thermostat that is not the case. Long run times is what give you efficiency and doing so at the lowest temperature to give you a comfortable temperature. A buffer is only inefficient when you are charging it to a higher temperature than you need on a fixed thermostat. As an example, I am using a 180L buffer, connected to a gas boiler and UFH. Have added loads of additional insulation to the buffer, buffer floats on boiler supply temperature (no thermostat). Boiler return flow temps don't go a over about 30 unless below -5, but with a min turndown of 6.7kW I get a decent runtime (even with an average 0.5kW demand). Efficiency of gas to heat conversion (gas meter to heat heater at the UFH) is +/- a little sitting at 105%, due full condensing all the time. Running the buffer at 34 on a thermostat gave around 95% efficiency. Even though run time was long, boiler return temps were higher. All the above is true for any heat source.

Or just get a suitable size for hot water and fan coils, you have to run ducts for a ducted system, so just as easy to run pipes.

Grant do an external volumiser that goes behind the heat pump. They also do a compact internal buffer/volumiser also. grant-combined-volumiser-low-loss-header-installer-uk-doc-0184-rev-1-0-november-2022 (1).pdfgrant-external-volumiser-installer-uk-doc-0183-rev-1-0-november-2022.pdf

Exhaust air heat pumps, i.e. those attached to a tank for heating DHW, seem to do a good job, get best CoP from taking internal air instead of external air. Some are coated tanks with require an anode changed annually 😥 but can cost the same a duplex stainless cylinders. A normal UVC and a smallish fixed duty heat pump would possibly give better reheat times. If your not careful you will have a house covered in external heat pumps. Any sort of heat pump is better use of PV than resistance heating as the CoP will always be better.

Should be easy, until you add in ventilation heat loss, which is a big variable. Does the sun poke its head out and give some solar gain...

Just takes a lot longer as floor response time is slower. So basically set everything as per loop lengths and adjust from there.

Want to get some things finished off outside, but weather here not playing, too cold

Trouble with the small area on their own zone, is what happens when they are the only zones opens - your number of litres engaged with the heat pump plummet and you get short cycling. Your better keeping as a single zone and balance the loops to get the correct heat in the rooms. Upping loop flow rate increases heat output of the loop, decreasing, decreases output.

Not completely - it's delta T. Just double checked, 58L at DT 5 gives 10 min run time, with output of 2.5kW and 0.5kW demand. Off time should be around 45 mins. With same DT and 1kW demand only need 45L Run time is dependant on DT Volume Heat output Heat demand.

Depends on direction, if tilted, if flat that's ok for summer, but winter out will be next to zero.

Think I worked out that a 2.5kW output and only 0.5kW heat demand, neef a heating system with a capacity of 45L, this needs to be always open to the heat pump, then your run time will be over 10mins. Which is therefore not shirt cycling. If you have loads of small zones that could shut off, you would need a buffer to meet or exceed the 45L.

Sound like you need a ventilation strategy, before you start making improvements other your house will start to turn black and your CO2 levels raise, all which will make an unhealthy home.

No the sarking boards have a gap, and the slates have a natural gap also. It's not normal to batten below natural slate in Scotland, but we have to install sarking boards.

If your flow through the loops is steady and the pump is a consistent steady noise (not noisy), then there is unlikely to be air in the system. You will hear air movement going through pump, if a blocked slug of air you get no water flow through that loop.