u/Electrical-Blood1507

I have an ecodan heatpump with an FTC6 controller. It has been working fine for 4 years since installed, however now it is failing to heat water intermittently. I will realise the water isn’t as hot as it should be, the controller is showing the immersion icon but water isn’t still sitting at around 30 degrees. When I restart the system the heat pump will eventually start up, run and bring the temp up to 50. This can sit for a few days with the heatpump doing the work, but then I find the water too cold again… so it seems the heatpump shuts down, immersion switches on but doesn’t heat the water. Only freed again by a restart. Does anyone know what the issue could be? I want to see if I can sort myself before calling an installer.