Gary68

I believe a 400L tank should have 2 sensors 1 towards the bottom and 1 towards the top, there is a setting in the hot water menus to set the cylinder to std or large. Large will mean it uses the bottom sensor if its set to std it will be using the top sensor only and only heating the top third of the tank. If you have enough HW this probably isn't the case but worth checking, the std and large settings are under DHW recharge in the menu

I have an Ecodan with a 210L tank we only heat once a day to 47C and don't reheat, its fine for 2 showers and a bath, with a 400L tank you definitely don't need to reheat during the day.

I think you need to go back to basics get someone to work out the heat loss for your house or do it yourself on the heat punk website then you can determine what your options are. Have you any idea why a 56kW heat pump was installed 19 years ago? It could be massively oversized like boilers are, you may only need something half the size or less. Why do you have a 300L buffer tank they are usually installed to keep oversized heat pumps happy with good flow rates which leads back to the first question.

Its nearly 20 years old, at the end of its serviceable life, are you not better off starting from scratch with a modern heat pump and redesigning the heating system as best you can.

In terms of internal noise and monoblocs I noticed you mentioned Mitsubishi, they don't have external pumps so the main pump and the noisiest one will be in your house, so I would avoid, I speak from personnel experience.

+2

Agree with John sounds like its plumbed incorrectly and its not getting hot as its just pumping the return water from zone 1 that is already cool. If you ramp up the flow temp to 45C and the ufh start to get warm then that would confirm it.

Mine does that too, I think its just the app. Do you have a mitsubishi preplumbed cylinder, if it was for 2 zones there should be 4 pumps in total, 1 for the primary circuit, 1 for each zone and 1 for dhw. If you turn both stats on to call for heat you should have 2 pumps lit up with lights if they are the std grundfos pumps that are usually on the cylinder

Are you saying that you can only heat zone 1 or zone 2 at once, or is just that you haven't got the thermostats calling for heat at the same time? If its the former then something have been wired up incorrectly. I have UFH downstairs and rads upstairs they are on separate stats and both can call for heat independently or together they just have different pumps for each circuit.

If you unscrew all of the actuators I believe that should open all the circuits as the actuators hold them closed so if the actuators aren't wired in correctly or they fail, then they will just stay closed.

Just another point for reference, we have a not very well built or insulated 190sqm house from 2003, heat loss was calculated at 7kw and have an 8.5kw Ecodan and it was fine at -6C last winter.

What is calling for 'heat', you may find that you need to increase the temperatures on your thermostats to call for heat which will tell the heat pump to turn on and then cold water will circulate round the system. That's how it works with my air to water heat pump.

Its an Ecodan, flick DIP switch SW2-4 to on, reboot system, cooling now available in heating menu select flow temp and away to go.

Mine is set to 48C and I can just about hold my hand under it continuously, so it sounds like you are a lot lower than that if the bath is just warm enough, at 50C you get burnt in 5 mins. Also depends where the temperature sensor is in your tank if its not towards the bottom a lot of the tank won't be at 52C

The Melcloud app is easy to program, just choose your unit, go to timer, I add in the start of the off peak time and till it to run at a fixed flow during the winter. The flow temp can only be set from the main controller not the app. Then at the end of off peak I tell it to run change back to WC. In spring and autumn, I still run it at night but only in WC mode so 32C rather than 45C in winter. At this time of year it probably won't come on till the next off peak period, so no peak use.