Most winter breakdowns we hear about start with something small: pressure that crept down, a condensate pipe that froze overnight or a thermostat with flat batteries. A few minutes of checks each month catches these early, and none of them needs tools or the boiler casing off.
Maintenance and servicing are not the same thing
Maintenance is what you do: looking, listening and keeping the system topped up. Servicing is what a Gas Safe registered engineer does once a year, opening the boiler to test combustion, clean parts and check the safety devices. You need both. Manufacturers say clearly which side owns what. Vaillant's ecoTEC pro operating instructions (document 0020244996) say "never attempt to carry out maintenance work or repairs on your product yourself" and call an annual inspection by a competent person a prerequisite, while Worcester Bosch's Greenstar i ErP user instructions (6 720 806 946) say "only a competent engineer can remove the appliance case".
| Task | How often | Who |
|---|---|---|
| Check the pressure gauge | Monthly, and after bleeding radiators | You |
| Look under the boiler for drips | Monthly | You |
| Check the condensate pipe outside | Before winter and during cold spells | You |
| Bleed and balance radiators | Start of the heating season | You |
| Check thermostat batteries and timer settings | Start of winter and when clocks change | You |
| Test the carbon monoxide alarm | Monthly | You |
| Annual service, filter clean, inhibitor test | Every 12 months | Gas Safe registered engineer |
Monthly checks through the winter
Pressure
Read the gauge with the heating cold. Worcester's Greenstar i ErP instructions say the system needs recharging if it reads less than 1 bar and give 1 to 1.5 bar as the target. Vaillant's ecoTEC pro instructions give a cold filling pressure of 1.0 to 2.0 bar and say the boiler switches off below 0.5 bar. Use the figure in your own manual, top up through the filling loop if it is low, and see our boiler pressure guide for what the readings mean. Needing to top up every month points to a leak or expansion vessel fault.
Leaks and drips
Look, without touching anything inside, at the pipes and valves under the boiler and at the pressure relief pipe where it leaves the wall. A wet patch below that pipe outside means the relief valve has been opening.
Display and noises
Note any code on the display, even one that clears itself, and listen for new kettling, banging or gurgling. Writing the code and the date down saves an engineer time.
Before the first frost: condensate pipe, lagging and power
A condensing boiler drains acidic water through a plastic condensate pipe. If that pipe runs outside and freezes, the water backs up and the boiler shuts down, which Worcester's instructions confirm. Vaillant's ecoTEC pro instructions say the condensate discharge pipe and tundish "must always be penetrable", in other words clear.
- Check the outside section is lagged with waterproof pipe insulation and runs downhill without dips.
- Clear leaves and debris from the end of the pipe and the drain it runs to.
- Lag exposed heating and water pipes in lofts, garages and outside walls.
- Leave the boiler's power on during cold spells and when you go away. Baxi's EcoBlue System manual says its built-in frost protection works "as long as there is power to the boiler", firing when the boiler temperature drops below 5°C.
If the pipe does freeze, thaw it with warm (not boiling) water or a hot water bottle, then reset the boiler. Our frozen condensate pipe guide has the full steps.
Radiators, controls and system water
At the start of the heating season, run the heating and feel each radiator. Cold at the top means air: bleed it, then recheck the pressure. Cold at the bottom or in the middle usually means sludge, which needs a flush rather than bleeding. If some rooms heat far faster than others, balance the radiators with the lockshield valves.
Check that the room thermostat responds, the timer shows the right time (especially after the clocks change) and wireless thermostats have fresh batteries. A dead thermostat is a common cause of "boiler not working" calls that need no engineer at all.
The water inside the system matters as much as the boiler. A magnetic filter catches sludge before it reaches the pump and heat exchanger, and inhibitor slows the corrosion that creates it. Baxi's EcoBlue System manual says the inhibitor concentration should be checked "at every service". Ask your engineer to clean the filter and test the inhibitor each year.
In summer
Modern boilers exercise their own pump if they have power: Baxi's EcoBlue runs it for 30 seconds a week without demand, and the Greenstar i ErP runs it for a few seconds after 24 hours. Running the heating briefly once a month in summer also keeps radiator valves from sticking.
Clear space, clear vents and a carbon monoxide alarm
- Keep the area around the boiler clear. Worcester's instructions warn "do not restrict this space with the addition of cupboards, shelves etc." because engineers need room to work.
- Do not block or cover any air vents in walls, doors or cupboards serving the boiler, and keep the outside flue terminal free of plants, sheds, bins and washing. Never adjust or wrap the flue.
- Fit an audible carbon monoxide alarm in the room with the boiler, test it monthly with its button and replace it when it reaches the end of its stated life. In England, landlords have had to fit one in any room with a fixed combustion appliance, such as a gas boiler, since October 2022.
- Clean the casing only with a damp cloth. Vaillant suggests a little solvent-free soap and no sprays or scouring agents.
The annual service and your legal duties
Once a year, a Gas Safe registered engineer should service the boiler. That normally includes checking the flue gases with an analyser, inspecting the burner, seals and heat exchanger, clearing the condensate trap, and testing the pressure, expansion vessel and safety devices. Ideal's Logic Combi2 installation and servicing instructions (UIN 236183) say servicing "should be carried out at least annually". A service typically costs £80 to £150. Our annual boiler service guide covers what is checked, how long it takes and how to prepare.
Servicing also protects your warranty. Vaillant's ecoTEC plus manual says the boiler "must be serviced annually" to keep the guarantee, and most manufacturers set similar conditions. Landlords have a separate duty under the Gas Safety (Installation and Use) Regulations 1998 to have gas appliances safety checked every year by a Gas Safe registered engineer and to give tenants a copy of the record.
You cannot service a boiler yourself. Combustion analysis and work on the burner, heat exchanger, seals and flue are legally Gas Safe registered engineer work. If you smell gas, turn off the supply at the meter if it is safe to do so, open windows, do not use switches and call the National Gas Emergency Service on 0800 111 999.
Signs your boiler needs an engineer now
- The same fault code comes back after 2 or 3 resets.
- The pressure keeps dropping, or climbs above 2.5 bar when hot.
- Kettling, banging or a new grinding noise that does not go away.
- Sooty marks or staining on or around the boiler or flue.
- The carbon monoxide alarm sounds, or anyone has headaches or dizziness that ease outdoors.
- Water dripping from inside the casing.