From cold the boiler fires up and gets the rads to temperature, it then shuts down and does not fire up till the rads cool down approx 1/2hr then fires up again for 15 mins to warm rads up again,continues doing this all the time.
have had an engineer out buts seems a bit lost
there is no room thermostat in the system just rad thermostats all fully open
have changed the pcb as advised but the same problem still exists with the new pcb
any ideas please