I believe our system is described as a Fully Pumped System "Y Plan" (3 Port Mid Position)
Gas boiler is an
Myson Heating Limited
Apollo 15/30, 30/50 and 65/80
Digital Room thermostat
Danfoss TP5 (the timer on the boiler has been set to constantly on to allow the room thermostat to control the timing)
More often than not the system will fail to heat the radiators needing to be over-ridden by moving the slide on the 3-way valve fully to the right. However, occasionnally the system will operate fine without intervention. This is only an issue when the thermostat kicks in. When the required temperature is reached and the thermostat switches off the slide returns to the left.
The original room thermostat was a basic honeywell dial and the boiler was used as the timer this was changed to the above digital thermo as an attempt to fix the fault. The fault however continue before during and after the change. The motor in the 3 way valve has also been replaced as an attempt to fix the fault.