Most boilers that fail in January were showing signs in October. A yearly service catches those signs, and on a condensing boiler it also keeps the efficiency you paid for. Here is what a proper visit includes, so you know what you are buying.
Combustion
The burner is checked with a combustion analyser, not by eye. Carbon monoxide, oxygen and flue temperature are measured and the gas valve adjusted to the manufacturer’s numbers. Combustion drifts as components age, and a boiler that was set up correctly five years ago is not necessarily correct today.
Heat Exchanger And Condensate
On a condensing boiler the heat exchanger and the condensate trap collect a film of acidic residue. The exchanger is inspected and cleaned, the trap is emptied and refilled, and the condensate drain and neutraliser are checked for flow. A blocked condensate line is one of the most common causes of a boiler locking out in cold weather.
Water Side
- System pressure checked and corrected
- Expansion tank charge tested against the fill pressure
- Air separator and automatic vents checked; zones purged of air if needed
- Water quality checked, and glycol concentration where the system has it
- Circulators, zone valves and mixing valves exercised
Safety And Controls
- High limit, low water cut-off and pressure relief valve proven
- Venting inspected end to end, including the termination outside
- Ignition components and flame sensor cleaned or replaced
- Outdoor reset curve reviewed, because the setting that was right for the previous owner may not suit how you run the house
- Error history read from the boiler’s own log
What You Should Get Afterwards
A short written record: the combustion readings, the pressure, anything replaced, and anything to watch. If a service visit ends with a sticker on the boiler and nothing else, it was a look, not a service.
When To Book It
Early fall, before the first cold week, so a part that needs ordering arrives before you need heat. If it has been more than a year, book it now regardless of the season.
Related: boiler heating systems we install and service · condensing gas boiler installation · boiler commissioning explained
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