PaulF11

We recently moved into a new build property with underfloor heating throughout and a Mitsubishi 8.5kw Air source heat pump to provide the heating and hot water. The house is a 4 bed detached property of 150m2. Each room has a Polypipe programmable room thermostat. These are on 24/7, on a comfort setting of 18.5°c from 6am until 11pm. Our setback is 17/17.5°c. We are having problems with the heating side of the system. When rooms are all up to temperature and no hot water is required, our Mitsubishi system will continually switch from pause to play despite no demand from any of the Polypipe room controllers. We have even switched the room controllers off completely but the ME system still switches on / off. The system is off for 1.5 minutes, then back on for 12 minutes before repeating continually. The cycle appears to be; the heating mode switches to pause and the heat pump in the garden stops, 2.5 minutes later the circulating pumps will stop for 1.5 minutes before the heating then switches to play, the circulating pumps start up and then fan outside starts up again and runs continually for 12 minutes. However, sometimes when the Polypipe room thermostats are searching for heat, the Mitsubishi Electric main controller for the Heat mode will switch to pause despite the rooms searching. Today, we had 1 room upstairs searching (it was at the comfort setting of 18°c but it had to achieve another 0.5°c to stop searching) and one room downstairs which required 1°c plus the 0.5°c to stop searching) The ME system is set up as two zones, zone 1 upstairs and zone 2 downstairs. The room upstairs has now achieved 18°c plus 0.5°c but zone 1 is still on play The room downstairs is still searching. Our Polypipe room thermostat manual states that they have a function called "Optimum Start" which is enabled on our controllers. It is meant to learn the warm up time of the room and start the heating at a time to achieve Comfort by the time required i.e 6AM. Our comfort setting runs from 6am until 11pm. Most days when a room is searching at 6am, it can take 12/15 hours to achieve an increase of 1°c by which time we've gone to bed and the we have the same situation the next day. We've had the house builders team of plumbers and electrician's here to investigate why the system is switching on/off but they can't resolve the issue. The plumbers have slowed the flow rates to 1 l/m, but the flow meters on the manifold don't move from 0 - are they not working or just not enough pressure now to move the gauge within the flow meter? What should the pressure be for UFH?