While you wait for answers, we may have found some information which could help you.
Click here for Apollo Myson 50Myson Apollo 30s plenty of hot water but rads only warm, ?
apollo myson 50?
My Myson thermostatic radiator valve is not working and will not open?
Myson thermostat won't click on?
MYSON APOLLO GAS VALVE?
How can I get a Myson thermostatic radiator valve to work?