JohnMo

Have had a thermal store and now have UVC, UVC wins hands down, way more usable hot water for the quality of water heated.

I hope not - as that exactly legal, they should extract and reuse or send for recycling. Then fill with new.

Think that's the crux of the issue. Driving gas and heating oil prices up and electric down per kWh makes the market move in a different direction. People start to insulate first, then look at different technology second.

Sizing for heat pump cylinders, the number in model number is size in litres

Think the heat capacity is nearer 7 than 12, looks like it can do 12kW if the brine is close to 20 degs, which is unlikely without geothermal.

It's GSHP and cylinder in a single container, not a gas combi.

Installers just see ASHP as a good reason to overcharge you, not sure it makes much difference what country you are in. Replace your combi unit with a heat pump cylinder, Ideal sell ones that are good and generally a low price. You only really need a 6kW ASHP. They can be picked for £2k or less. You need a 3 way diverter valve. A plumber for a day or two. Or you may be able tap the ASHP into the water circuit of your combi, so can utilise the cylinder and buffer, but control the 3 way valve by the ASHP.

Why not download the instructions? Primary bypass is important, with a buffer you need a balanced flow either side of the buffer, without a buffer you have to maintain a minimum flow to keep the heat pump happy. Primary bypass in a min flow valve. Secondary is how much mixing occurs between incoming hot water and return water.

My view is keep things simple. Never really seen the point of ducted ASHP pipes, when you can simply come through the wall then clip pipe to wall and insulate very easily. You seem to devote two rooms to plant, consider merging into one room. Do the MVHR inlet and outlet on the same wall otherwise you encourage a mismatch of pressures and unbalanced flows depending on the wind. Consider a combined directional grille, if it simplifies duct routing. You need drainage for the MVHR unit as well. Not sure why you need a radiator in a plant room, when you have the UFH manifold and cylinder in same room. Consider bringing inverter inside Don't buy into the put the ASHP on the south side, they consume so much air it's ambient air temp they see and half their life its dark anyway.

That's why you CoP isn't great, you need to start to reduce that flow temperature, ideally set up weather compensation. Start by dropping the flow temp a couple of degrees leave for 24 hours and note down what if any has changed and outside average temp, keep doing this until the house temp drops a and doesn't recover back to 21, then add a degree back on. Your flow temp will be more likely be in the mid 30s than 50.

Or a simple Willis heater if easier to hook up.

Maybe check the temperatures in a hour or soto see if things change.

In normal operation you shouldn't hear bypassing water, as the UFH starts to close down, it should start to open. The valve volume increases as the valve is just about closed, then goes silent once completely closed. Sounds like your pump setting was ok.

Welcome, not good about the builder. Post your question the appropriate area, keep each question to the point, otherwise you will get a lot of varied responses.

3.8m.is .38bar, plus piping pressure losses, so it's likely the pump is just pushing the bypass open. You should be able to here it passing. Get everything up and running and slowly increase the setting until you cannot hear it passing. You should also adjust pump speed, reduce setting until flow rates at the UFH drop a little.

Sounds like a typical 4 port buffer, with a decent mismatch in flow rates, so plenty of mixing going on.

Realistically you need a 6kW heat pump, not sure a 4 kW would be big enough. With that size (6kW) heat pump and a 210L cylinder we are basically heating it once per day and it takes 45 minutes. There is plenty of capacity to do heating as required. A bigger cylinder a couple of heats a day would make the heating times short enough. We are using a 6kW on a smaller heat load (smaller house) and it just stops and start as required, generally runs for about 10 mins on and 10 to 15 off on a mild day, may run a few hours when cold. Our ASHP ramps up and then down, no issues. Just plumb exactly the same as your gshp was.

So the way the buffer is supposed to work. Hot water from ASHP goes in to top port, and out the other side pumped by a pump, return water from heating system go in to the bottom port, the heat pump pulls the water from other other bottom port. In a ideal world the flow either side of the buffer is equal and supply and return water never mix. The temperature in the centre of the buffer should see the mean temperature of the flow and return. Some mixing of the flow and return will move the reading temp up or down. The more unbalanced the flows either side of the buffer the more mixing that occurs, this requires a higher flow temperature from the heat pump than is delivered to the heating system to compensate. Resulting in a drop in CoP.

How do you operate at the moment?

Confused now

If your boiler is happy and it must be as it's running, then it should be be ok to leave as it is.

What do you mean? If you have an easy route to the snug ignore my previous comments about cascade. You need to look at the airflow where the air is coming from, if you only extract from the toilet the air could just short circuit under the the utility and WC doors and miss the utility out

You can only really do it with thick screed and use it as a storage heater. Over charge the floor you are hot all day, under charge you are cold all day. It's a fine balance to get it right. You need to stop heat input earlier than you think as well

Another couple threads on the same subject started in the last couple of weeks, have a search.

How is buffer plumbed in 2 ports or 4 ports? And where are you measuring temperature on the buffer? Really you set it for weather compensation, to get the best economy out the heat pump. A set flow temp could be cost you money on anything the coldest day.