All of the hot water in the house is supplied via a gas boiler and connected immersion tank. As one bathroom is at the far end of the house, and we wanted to get a good pressure for the shower, we got a pump installed some years ago that pumps both the hot and cold water to that bathroom - so the water to the sink, bath and shower are all pumped. Everything has worked fine until recently when we found we can no longer get any hot water in that bathroom. We have hot water everywhere else in the house, just not at all in that bathroom. It is the only water supply connected via the pump.
The water feeding the bath and shower goes through a thermostatic mixer valve with 3 dials (on/off shower, temperature regulator, on/off bath) and the water feeding the sink is through a separate mixer tap. The pump starts up when any of the taps are turned on and turns off a short while after the water tap is closed.
Irrespective of which tap is used (sink, bath or shower) we get cold water, and this is also irrespective as to which way the sink tap or thermostat (for shower or bath) is turned. If it is turned to the hot only side, we still get cold water and the pump operates.
I would have thought that if there is a problem with the hot water feed (e.g. an airlock) then we would get no water when the tap/thermostat is turned to hot - but we get cold water irrespective as to the temperature setting.
Does anybody have any suggestions as to what could be causing the issue?
Many thanks in advance for any help.