Beelbeebub

Yes but if the vessel has never been topped up from new this shouldn't be a possibility as they are generally precharged with dry nitrogen - strictly speaking they should only be topped up with dry nitrogen, but nobody bothers. There would only be enough water from condensation to squirt out if it had been topped up a few times, which would indicate an issue somewhere (eg leaking prv) anyway.

If the system pressure target is 1.5bar when cold, then your pressure vessel should be at a little bit below (say 1.4bar) when empty. This allows a little water into the vessel when at system pressure and the maximum volume change when hot. So if your water pressure gauge shows 0.2bar your vessel should show 1.4bar. Of it shows lower then the pressure is wrong. You can top it up but the fact the air has been lost points to a failure in either the valve or the internal membrane. If some water comes out of the valve, your membrane is almost certainly shot. Swapping the vessel is the easiest.

2 possibilities You have a leak somewhere You may have an issue with the expansion vessel (red tank) First check the expansion vessel When the pressure is near zero, like in the first picture, get a tyre pressure gauge and read the pressure in the red cylinder. There should be a valve exactly like a car tyre one on the top. It should be something like 0.7bar, 1 bar or similar. If it has pressure eg 0. 7bar but the gauge on the water reads near zero, it is possible you have a leak somewhere. If it reads near zero your expansion vessel has lost has pressure (you may still ha e a leak but it's a bit less likely) If the latter you can pump it up with a.tyre or bicycle pump. Then top it up with the flexi hose. You need to turn the. Slotted screwdriver thing so it's. Inline withe the pipe, then turn the black handle at the other end. There should be a whooshing sound and the pressure creep up. Once at desired. Level (1 - 1.5bar) turn both valves off and disconnect the pipe (get a saucepan under as some water will come out. Beware just topping up the pressure continuously. The water is going somewhere!

You usually need to buy the camera too, I use thr "top Don" one, it just plugs into your phone and away you go.

The ufh should be able to get those rooms warm if it did before. The flow temp shouldn't be very high ie a HP should be able to achive the temps. My suspicion is too. Much flow of going via the radiators, which is shutting down your HP, the UFH then doesn't have a supply of warm water to "top up" the loop temp via the mixer valve and then they underperform.

I had a cottage where the radiator in the hall was absolutely scorching and all the other rads were like warm. The boiler short cycled and lots of gas was burnt. We closed the valve on that rad right down and all the rads became warm, the boiler stayed on for long continuous burns and the cottage was warm for not much more money

As I said the other option is one rad being "too open" and starving the other ones.

Either your emitters are very undersized - thr ufh loops should be OK, the whole. Point of ufh is it being a big emitter. Maybe your rads are too small? What type are they? Single panel, finned? Double panel double fin?. How big are they? Rads for HP should be bigger than what is typical in a boiler heated house. Your plumber should be able to tell just looking - 'they look bigger than I wound expect" or "nah, looks. like I. Would expect for a gas boiler house" (ie too small!)

Potentially the Vito boiler was supplying higher flow temps and each emitter was outputting more. This is why radiators and pipes sometimes need to be swapped for bigger ones when a HP is installed. Get an IR thermometer (better yet an IR camera for your phone - can use it to track down heat leaks in the walls too) Check your rads, your (heated) floors. Is there a rad that is especially hot, in particular if it's flow and return are very close - they should be 5-7C different. It's possible one of the rads is "short circuiting" the flow, which cause the HP to shut down (as the flow and return are too close) and your overall heat output to buikding is lower plus less efficient because of start stopping.

Link to the manual. https://trade.centralheating.co.nz/assets/resources/Chofu-Operating-Installation-Manual.pdf

What are your radiator sizes? Are the ufh heated rooms warm enough? What is your floor temp in those rooms(cheap laser thermometer will do) Look at what the return temp (parameter 00) and output temp are (09). Ideally they should be 5-7C apart. If the return is climbing closer to the output then your emitters aren't getting rid of the heat quick enough. It could conceivably be a radiator loop that is too open and the flow is all rushing thorough there, hardly losing any heat.

This may not be a good idea, temps that high may cause issues with the slab and floor coverings - the mixer and pump system is there to run the UFH at a lower temp than the rad system. IIRC thr max floor temp is supposed to be 28C, running at those flow temps will almost certainly result in parts of the floor getting hotter than this.

The suction temp is the temp the refrigerant gas is when it leaves the outside coil and enters the compressor, it is then compressed and leaves as a hot gas (discharge temp) So a suction temp of 4C means the air moving over the coil outside was probably at about 4C Then 88C gas was leaving the compressor. Which seems a bit high for heating mode, I would expect it to be more like 50-55C for a 45C (water) flow temp. That suggests something might not be quite right.

The first thing to note is that this sub zero weather will cost alot to heat especially with a HP. For example, my gas consumption is about £8 a day in these conditions. You say parameter 21-00 is set to 0. This is fixed flow temp. Look at parameter 20-01, that should be the temp your HP is outputting. The default is 45C, and maybe that is too low? It will also have been too high for the milder weather. The default for 21-02 is 45C, so the fact it's been set to 50C implies someone has changed it - possibly because your heating system needs more than 45C in these conditions.

Could you install something between the cylinder sensor and HP that basically tricks the HP that the cylinder is at temperature after a power cut? Depending on the sensor it could be as simple as a relay and resistor.