Worcester Danesmoor 26/32 lockout - frozen fuel?

Hi

Since the cold weather started my heating has had an intermittent lockout problem. Before lock out the system becomes noisy and there is a smell of unburned fuel. I called a local heating engineer and asked for a service. I explained the symptoms and the engineer told me it was probably frozen fuel (gelling). The oil tank is north facing and exposed. The feed from the tank is lagged.

The guy spent 20 minutes doing the service and told me it was OK and no new parts were required but might need a new 'nozzle' in a year or so. He had the heating running but it was in lockout!

I am not too happy at the result. Fair enough if the oil is frozen he probably can't do much about that but 20 mins to do a service seems too short. I feel like I might have been ripped off.

Also is it possible to service the heating properly when it isn't working?

What kind of bill is reasonable for this 'service'.

Thanks