JohnMo

Doesn't that end up giving a very biased outcome, you miss the 100's with zero issue, but you get the ones with issues, whether caused by poor workmanship, poor selection of product and or project. Then you need to differentiate the two routes of a self build a 'self build', and the custom build. One is the actual person doing the build, the other paying a professional to do it them, with no real participation in the hands on stuff. All the above with have a different thought processes, maybe similar outcomes maybe not. You also need to include bankruptcy and people's money being taken - real issue.

Pressure safety group and an expansion vessel. Inhibit the water with a corrosion inhibitor and Y type strainer. Take out any flow restrictors in the normal cold feed.

Back to the boiler, where the cold water would go in. So a closed loop with an external pump, into the boiler where cold water normally goes in and out where hot water comes out, pumped through a cylinder coil. Almost the same as a 4 pipe system boiler?

Makes you wonder if you could simply strap an external pump on the DHW pipes and charge a cylinder. Use a heat pump cylinder at 14 to 16l/min - same as 6kW heat pump. Then leave the CH on WC.

That's the idea.

@SimonD so maybe a daft question, and out of interest - is a 4 pipe boiler such as the Viessmann, basically a combi boiler with a pump on the DHW side? So instead of taking in fresh water, uses system water to heat the cylinder?

Can I ask, why just Polystyrene ICF, wouldn't your output be more rounded if you also looked at woodcrete ICF also?

Storage heaters on E7 in main areas and panel heater in bedrooms? E7 Cylinder. But why? I would do self install of a heat pump - and UFH and heat pump cylinder. UFH on 200mm centres generally, 100mm centres in bathrooms, single zone, no buffer, flow direct from heat pump or electronic mixer. Overall could be cheaper to install and run. All out of sight. 4 to 6kW heat pump - £2k Cylinder - £800 UFH manifold - £100 Pert-al-Pert pipe for UFH £400-500 with clips and unions Another £500 for general stuff All VAT free Bungalows cost more to heat than houses as the form factor is rubbish, direct electric heating will cost huge amounts. Don't be fooled by advertising that is there to mislead. Do the heat loss calculation, if your house looses 3kW, that's 72kWh per day or £20 per day or £600 per month, plus DHW heating. Even a poor install of the heat pump will give a CoP of 2.5 to 3, so now your monthly cost is £200.

Would suggest you are overthinking something here. You system is what it is, low loss header no point, but you have one, unless really well designed specifically for your system they reduce efficiency. But you have what you have. If you are concerned with running out of hot water allow more time slots for heating. I heat once in the morning and again in the afternoon (but it will only add heat if needed by the thermostat), you could just as easily allow it to heat anytime based on thermostat thermostat. If you aren't consuming the thermostat will get to temperature and stop the heat cycle. Unless you are willing to pay a huge amount of money out, to get a plumber in and pull your house apart, just use your thermostat, the timer you have - done

Looking at the datasheet you are likely going to need one on the cold and the other on the hot pipe, so twice the cost. Only really useful for combi or unvented cylinder. What have you got?

Just looking at the photo, your issue could be the vertical section of pipe from the cylinder coil to the 3 port valve. Very likely you have a nice internal current in that pipe. Ideal would be to take the pipe down 150mm then up to the valve. That would eliminate any likelihood of a thermosyphon.

To allow me to run the summer house temperature at the most economical temperatures and be at the right temperature at the right time, I have added a thermostat. The thermostat sets two different flow temperatures on the heat pump rather than switching off the water flow. The first is ok for a set back temperature, but also more suitable for house heating, the second temperature is 2 degs hotter (may need to adjust) and is more suited to the garden room. Now have a simulator for a DHW probe installed and this has freed up a set of contacts to allow the double set point on the heat pump to be used. So when make contacts (via the thermostat NC contacts) the lower set point is set, when break contacts (thermostat demand on) another temp set point is set.

So took the time to install my simulator for a cylinder DHW probe and it works a treat. 5.6kΏ resistor across two terminals of the wiring centre and a 15kΏ resistor connected to normally closed side of a relay. A call for heat opens the relay contacts and the heat pump thinks the water in the cylinder is 42 degs, so starts a heat cycle. Once the thermostat on the cylinder is happy the relay contact closes and the heat pump thinks the cylinder is at 51 degs. The cylinder and heat pump are not connected to each other a wireless MainsLink switch. This has released a set of contacts that now allows a double set into be used and two WC curves. 62c460aeda4aa444DS-MAINSLINK-9.pdf

I found from my install of an ASHP, little changes can make a dig difference to how much electricity you use. There are several ways to have the circulation pump run, for example. Recently changed mine from continuous to intermittent as decided by the internal temperature controller. Thought it may save some energy - but just the opposite An image of the electric consumption but shows the ASHP starting and stopping. The left three peaks are letting the heat pump control the circulation pump, the other wider spaced peaks are circulation pump on all the time. First three peaks is the ASHP short cycling, plenty of electric going in not much heat coming out. The other two peaks show longer run times, but also long off times. It was 8 degs at the time and heat pump running very low loads. The main take away from the above, is you need to take the time to understand how your heat pump is running to get the best out of it. (Most heat from least electricity). Have also found leaving to run all the time let's you lower flow temperatures so you use less electricity.

The cylinder consists of 1. An outer metal jacket/casing - decorative cover. 2. Then insulation 3. Then the cylinder. I drilled in item 1. Then with a drill bit in fingers removed the insulation until I touched the cylinder 3. You don't drill into item 3. The probe butts but against the cylinder wall and you get a slight under read.

My attempt. Cheap eBay sensor with a 6mm probe. Drilled 4x 6mm holes in casing of the UVC down to 50% height. The 3rd one down coincides with the height of the secondary returns. There is about 4 deg under read compared to the thermostat pocket. But all good enough to get an idea of the hot water left in the cylinder. Especially good for a slim line cylinder. Night before temporary mounts with tape. Showing level of hot water (bottom gauge reads 20 degs)

Good sun day today. Battery fully recharged by lunchtime, left heat pump running and 2kW going into hot water via immersion at one point. Grid power is excess going back to the grid on the battery software, but really it goes direct to hot water via a diverter. It's plotted every 5 mins so peaks are missed. Wife just put the washing machine on, to use more electric.

ESBE make a few versions, I got an ESBE CUA110, super cheap of eBay and the three port valve and actuator. Just run Salus auto balance actuators on each loop, always powered on to give a fixed dT. Removed all the room thermostats as they just added nothing to control of room temps. Just have a single thermostat in the hall.

Sort of, but it runs in the background weather compensated. Heat pumps cycle at low loads, so the average flow temp drops anyway. So although mixer is trying to control 28,if the flow is below 28 because it on an off cycle it gets what it gets. So mean flow temp through the UFH drops. The ESBE mixer has two set points, T and T2. So have a house thermostat set at 20, above 20 the ESBE runs at T and targets 28 deg, if the house drops below 20 (sub zero temps), it goes to T2, which is set to 36, so it can take whatever the flow temp from the HP which is based on WC curve. The WC is set for the fan coil.

That's a lot of pipe and a lot of loops. My 6kW heat pump circulation pump has a duty point 16L/min, which my 7 loops and fan coil use the rate up. Your issue will be having the flow rate available to satisfy lots of loops and radiators. Mixing down from 35 to 26 may actually get you out of hole, as there will be lots of water recycling within the UFH system instead of all going through the heat pump, which I think would start to cause issues requiring a buffer and additional pumps. Defrost don't seem to an issue, with a mixer, because it takes the heat required from the return water, I believe.

Really doesn't make a huge difference once flow temps get below 30. I am on 300mm centres and have the flow set at 28 in to the UFH via a mixer. If I was at 100mm centres I think my flow would have been 26. The other issue not talked about is you cannot get the heat pump to run reliably below 30 anyway with UFH (or I can't). Reason is the heat pump does cycle on off at low loads, it requires around 8 degree temp difference between target and return temp to initiate a restart. House is at 20.5 degs, floor is slightly warmer. So if I run the heat pump at 28, I need the return flow at below 20, which is cooler than the floor and cannot happen. First time I tried, heat pump ran for an hour, got to target temp and stopped, then sat idle for the next 12 hrs as the floor was never going to drop to 20 degs or below as the house was warmer than that. So I run a slightly elevated temperature and mix down to 28. Or you batch charge the floor at an increased temperature and use as a storage heater.

It would be unusual to have a mixed system without a mixer on the UFH. Get a suitable mixer for for low flow temps, ESBE electronic or IVAR low temp mixer and you can flow any temps you like elsewhere. Something like the ESBE mixing doesn't need any mixing so for me works better. I flow between 30 and 36 to a fan coil and 28 into the floor without issue using the ESBE. You zero need for a buffer. If you are well insulated your upstairs rads may never come on anyway.

It is an issue, no ideal of a practical way to fix - your stair will be sucking heat away from the house for ever more.

Really wouldn't bother doing movable panels, the complications aren't worth the effort. Just decide what you want out the system. I wanted decent winter performance, not really bothered about loads of excess generation, I can't sell in the summer. So I went vertical panels, they are good in winter (if the sun's out) and pretty good in summer.

Won't worry over it, just run at a lower temperature - problem fixed.