I have just moved from a modern house to a 60's bungalow and am struggling to understand our new CH system. So far we have had a CH engineer out twice when the system stopped producing hot water.

I am puzzled at the hot water capacity. It only will produce about 2/3rd's of a bath worth of hot water. Having managed this the flow of hot water dwindles to a trickle, and also strangely the flow of cold water also dwindles to a trickle as well.

Why is this? Surely the cold water is at mains pressure so should continue to flow regardless of the state of the hot water system?

I also would like to know about the system's control thermostat. Are room thermostats interchangeable and can I simply replace the existing one with a programable one? Do they simply act as a relay to the main system, making a low-voltage connection or are they actually switching mains voltage? Presumably if they are a simple low voltage switch they could be activated by a HA device as a means of switching the CH on and off?

I believe many CH controllers use a standard mount plate wired in a particular way. I am surprised that this fact hasn't been used to mount a HA controller on the system instead of the standard timeswitch controller or am I mistaken?