Question from Gerald Wicks, via e-mail:
In the Benchmark log book for domestic gas boilers, it asks for the differential temperature of the flow and return pipes. When should these readings be taken?
Answer from Martyn Bridges, director of marketing and technical support at Worcester, Bosch Group:
The differential should be measured at every radiator and at the boiler, to undertake this it would be advisable to follow the process below:
Turn the boiler on, then turn the boiler thermostat up and the room thermostat up.
• Close any system or boiler bypass
• Turn the TRV on the radiators to maximum
• Allow the system to run for at least 20 minutes
• Using a contact thermometer or a differential thermometer, adjust the lockshield valve on the radiator until the correct differential has been achieved, (generally 20ºC for a condensing boiler and 11ºC for non condensing)
• Undertake this on all radiators
• Adjust system bypass to achieve the same differential.