Since the annual service of my traditional gas boiler the house takes considerably longer to heat up. The boiler flame no longer seems as "fierce" as previously. I'm told the burner pressure and temperature flow rates on the boiler are correct and that the input gas pressure is just about within the expected range. However it was observed (in passing) that the input gas pressure does fall "significantly" when the boiler calls for heat compared with the gas pressure being delivered to the boiler when it's off.
Could this be causing the problem? Is this something that can be fixed? Does it mean an adjustment, a new part or a complete new boiler?