Can anyone please help my husband and I who have been trying in vain to get our central heating to come on for the first time since the summer months. We have a Potterton Flamingo 50 (probably 20+ years old) and have set both the thermostat knob on the boiler and the room thermostat turned up high. The boiler main burner fires up for a minute or two but then cuts out, followed by a loudish "ping" noise from the boiler. The pilot light stays on. Funny thing is we have hot water but can't understand how as the main burner is not on for that long. The boiler will continue with these short bursts while the timer is on. We had a new pump about 4 years ago and had the thermocouple and injector pilot replaced 2 years ago. Does anyone have any suggestions of what we could try or is it time to call someone in?