On this page
- Why do boilers develop problems in summer?
- Which faults stay hidden while you only use hot water?
- How do you run the heating in summer without wasting gas?
- What summer boiler problems should you not ignore?
- Is summer a good time to service your boiler?
- Booking a summer boiler service in Stoke-on-Trent
- Frequently asked questions
Quick answer
In summer, boilers sit idle for months, so pumps and diverter valves can stick, and faults on the heating side stay hidden while you only use hot water. Run the heating for a short spell once a month, keep the boiler powered, and act on any leak, pressure drop or fault code rather than waiting for autumn.
Key takeaways
- Pumps and diverter valves can stick after weeks without moving.
- Using only hot water hides faults on the heating side.
- Run the heating briefly once a month and leave the boiler powered.
- Summer is the quietest time to get a service or repair booked.
Summer should be the easy season for a boiler. It is only heating water for taps and showers, and the radiators have the months off. But idle parts are exactly where some faults start, and others simply go unnoticed until the first chilly evening in October, when everyone else is booking an engineer too.
Why do boilers develop problems in summer?
Mainly because parts stop moving. The pump, the diverter valve on a combi, and zone valves on a system boiler can sit still for weeks. Deposits and sludge settle, seals dry slightly, and parts that moved freely in March can be stiff or stuck by September.
Many modern boilers guard against this by briefly running the pump and moving the diverter valve at intervals when they have not been used. That only works if the boiler has power. Switching it off at the fused spur for the summer stops that protection, so unless the manufacturer advises otherwise, leave it powered and simply turn the heating off at the controls.
Which faults stay hidden while you only use hot water?
On a combi, a boiler that makes hot water happily all summer can still have a faulty heating side. A diverter valve stuck in the hot water position, a seized pump, a failed room thermostat or cold radiators will not show up until the heating is called for, usually on the first cold day.
On a system or regular boiler with a cylinder, the heating zone valve can fail in the same way while the hot water zone works normally. The reverse also happens, and is covered in no hot water but the heating works.
| Summer habit | What it can hide or cause | Simple fix |
|---|---|---|
| Heating off for months | Sticking pump, diverter or zone valve | Run the heating briefly once a month |
| Boiler switched off at the spur | Anti-seize functions cannot run | Leave power on unless the manual says otherwise |
| Only using hot water | Cold radiators, faulty thermostat | Test the heating before autumn |
| Ignoring slow pressure drops | A small leak getting worse | Check the gauge weekly and get leaks looked at |
| Putting off the service | Parts needed at the busiest time of year | Book in summer while engineers have availability |
How do you run the heating in summer without wasting gas?
Once a month, turn the room thermostat up above the room temperature for around ten to fifteen minutes, check the boiler fires, and feel whether the radiators start to warm. Then turn it back down. That moves the pump and valves, and it tells you the heating side still works.
It uses very little gas, and it is a far cheaper way to find a fault than discovering it on a frosty morning. If one radiator stays cold or is cool at the top, bleed it; if several stay cold, make a note for the engineer.
Set a monthly reminder on your phone for the first weekend of the month. While the heating runs, glance at the pressure gauge, listen for new noises and check under the boiler for drips. It takes five minutes.
What summer boiler problems should you not ignore?
Do not ignore leaks, pressure that keeps dropping, fault codes, new noises, or hot water that swings between hot and cold. These do not fix themselves over summer, and most get worse. Anything involving gas smells or signs of poor combustion needs acting on immediately.
- Pressure dropping with the heating off. Points to a leak somewhere in the system or boiler.
- Water under the boiler. Seals, pump or pressure relief valve, all engineer jobs.
- Hot water temperature swinging. On a combi in a hard water area, often scale on the plate heat exchanger or a flow sensor issue.
- New noises. Kettling, grinding or whining can mean scale, sludge or a failing pump.
- Repeated lockouts. Even on hot water only, see our guide to why a boiler keeps turning off.
- Soot, staining or a yellow flame on older appliances. Possible poor combustion; stop using it and get it checked.
Carbon monoxide does not take the summer off. Keep a working CO alarm near your boiler and test it. If you smell gas or suspect carbon monoxide, turn off the appliance, open windows, get outside and call the National Gas Emergency Service on 0800 111 999. Never remove the boiler casing.
Is summer a good time to service your boiler?
Yes. Engineers have more availability in June and July than in October, you do not need the heating during the visit, and if the service turns up a part that needs ordering, there is plenty of time to fit it before the weather turns.
Some routine summer care, such as bleeding radiators and checking controls, is covered in our summer boiler maintenance tips. The service itself is best left to a Gas Safe registered engineer, who will run the heating and hot water, test safety devices and check combustion.
Booking a summer boiler service in Stoke-on-Trent
A standard boiler service in Stoke-on-Trent is £90, and summer appointments are usually easier to get at a time that suits you. If something is already wrong, our engineers can diagnose it on the same visit.
We also cover the Derbyshire side of our area, including boiler service in Ashbourne and boiler service in Matlock. Call 07896 677083 to book.
Frequently asked questions
Should I turn my boiler off completely in summer?
Usually no. A combi still makes your hot water, and many boilers need power to run their anti-seize and frost protection functions. Turn the heating off at the thermostat or programmer instead. If you are going away for a long period, check the manual for the manufacturer's advice before switching off at the spur.
Why is my hot water hotter in summer?
The water coming into your home from the mains is warmer in summer, so a combi has less work to do to reach the set temperature, and at low flow rates it may overshoot slightly. If the water becomes scalding or the temperature swings sharply, that is worth having checked, as it can point to a sensor or scale problem.
Does a boiler use gas in summer if the heating is off?
A combi only burns gas when you run a hot tap, unless a preheat or keep-warm setting is switched on, which keeps some water warm for faster delivery. A system or regular boiler will heat the cylinder on its hot water timer. Check your settings if gas use seems higher than you expect.
Sources and further reading
Gasmaster Plumbing & Heating has served Stoke-on-Trent since 2005. Every article is written by our Gas Safe registered engineers (reg. 220932) from day to day work on boilers, heating and gas appliances across Staffordshire, Cheshire and Derbyshire.
