Quick Answer: Leaving your central heating completely off from May to September is the leading cause of October boiler breakdowns in West London. Over summer, mechanical seals settle, circulating pumps seize, and Thermostatic Radiator Valve (TRV) pins stick shut. By running a simple 15-minute heating test in late August or September, you exercise the pump impeller, move the diverter valve, and can easily catch stuck valves before the first cold snap hits. It costs nothing. It just takes 15 minutes, and it can save you a breakdown callout during the busiest week of the engineer’s year.
Key Takeaways
- Test your heating for 15 minutes in late August or September to unstick dormant components.
- The boiler gauge should sit between 1.0 and 1.5 bar cold. Top it up via the filling loop if it dropped over summer.
- Stuck TRV pins: if one radiator stays cold, the valve pin is likely stuck. Tap it gently to release it. Never pull it out with pliers.
- A humming boiler with no heat reaching the radiators points to a seized pump or diverter valve.
- If the boiler fails the test or pressure drops instantly, contact us for a fixed-price repair before the winter rush.
Why Do Boilers Break in October?
Every October in West London brings the first real cold snap. Heating engineers are immediately flooded with emergency call-outs. Nine times out of ten, these are not sudden catastrophic failures. Nothing breaks overnight. They are the result of the heating system sitting entirely dormant for four to five months.
When central heating components stand stationary over summer, two things happen. First, magnetite sludge and corrosion debris dry out and settle in the pump and valves. Second, mechanical rubber seals and metal spindles seize in place.
When you suddenly demand full heat on a cold October morning, these seized components burn out. The pump and motorised diverter valve take the worst of it. Their motors strain against a spindle that hasn’t moved in months, and they burn out trying to free themselves.
How to Run the 15-Minute Heating Test
You can prevent most of these start-of-winter breakdowns. Run this test in late August or September.
- Look at the pressure gauge on the front of your boiler or the digital display. When the system is cold, it should read between 1.0 and 1.5 bar. If it dropped over summer, repressurise it using the filling loop.
- Walk around the house and turn every Thermostatic Radiator Valve (TRV) up to its maximum setting.
- Set your main wall thermostat to 25°C. This sends the signal to the boiler to fire up the central heating.
- You should hear the boiler fire and the pump start humming. After a few minutes, feel the pipes feeding your radiators. They should all start getting warm.
- Once you confirm everything works, turn your thermostat back down and set your TRVs back to your preferred room temperatures.
Troubleshooting Faults
Running the test early gives you time to fix issues before you need the heating. No panic, no queue for an engineer. Here is the exact diagnostic sequence we use to triage common post-summer faults.
One radiator stays cold
Stuck TRV pin
DIY-safe: tap it free yourself
Pressure shoots up then drops to zero
Failed expansion vessel
Gas Safe engineer only
No heat, hot water is fine, combi boiler
Seized diverter valve inside the casing
Gas Safe engineer only
No heat, hot water is fine, system boiler
Seized or electrically faulty zone valve
Check the manual override lever yourself, then a Gas Safe engineer if it’s mechanically seized
A Single Radiator Stays Cold
If the rest of the house warms up but one radiator stays completely cold, you likely have a stuck TRV pin. This is incredibly common after summer.
Remove the plastic TRV head. Most just unscrew. You will see a small metal pin sticking out of the valve body. Tap the side of the valve body gently with a spanner, or press the pin down with a flat tool until it springs up freely.
Never pull this pin upwards with pliers. If it comes out completely, the internal water seal breaks. You get an uncontrolled leak.
The Boiler Loses Pressure Instantly
The boiler pressure might sit at 1.5 bar cold but shoot over 3.0 bar the moment the heating turns on. It often dumps water out of a pipe outside. Your expansion vessel has probably failed or lost its air charge. When the system cools back down, the pressure drops to zero, and the boiler locks out. Not a DIY fix. An engineer will need to recharge or replace the internal vessel.
Boiler Fires But No Heat Reaches Radiators
You might have reliable hot water from your taps, but the radiators stay stone cold even with the thermostat turned up. The boiler itself is working fine here. Fault lies with the controls.
On a combi, the likely culprit is a seized diverter valve. It sits sealed inside the boiler casing. Don’t open the casing yourself. Only a Gas Safe engineer can access and replace it.
On a system or heat-only boiler, look for a failed motorised zone valve instead. This is a separate unit, usually mounted on the pipework in an airing cupboard, not inside the boiler. Most have a manual lever on top for exactly this situation. Flip it to override the motor and check whether the valve body itself moves freely. If it does, the fault is electrical. If it doesn’t, the valve is mechanically seized. Either way, the motor or spindle will need replacing by a Gas Safe engineer, but the lever check tells you, and us, which fault you’re dealing with before anyone arrives.
Keep Your System Healthy
The 15-minute summer test is your best defence against the October rush. Run it in late August or September. If it flags an issue, get it sorted before the cold weather sets in.
If you rent, you don’t need your landlord’s permission to run this test. None of it touches gas components, so it isn’t Gas Safe work and doesn’t need a CP12 visit. Only book that if the test uncovers something that does need an engineer.
Our Gas Safe registered engineers (657972) cover Harrow, Wembley, Fulham and across West and North West London. Every job is backed by a 12-month workmanship guarantee and a fixed written quote, and our line is answered 24/7.
Book your annual boiler service online or give us a call on 020 8051 2124.
Related reading
- Radiators not heating up after summer
- How to bleed a radiator
- Boiler making a noise?
- Central heating services
- Areas we cover
Frequently Asked Questions
Should I turn my boiler off completely in summer? No. You should leave your boiler powered on over summer so you still have hot water. For the heating side, turn your room thermostat down. Many modern boilers include a built-in pump anti-seize protection feature, documented in manufacturer installation manuals such as Worcester Bosch’s Greenstar range, which briefly runs the pump on a set interval. This only works if the boiler is left on.
How often should I run my heating in summer? Running your central heating for 10 to 15 minutes once every month during the summer is enough to prevent the pump and valves from seizing.
Why is my boiler pressure dropping over summer? Small, unnoticed leaks on radiator valves can cause the pressure to slowly drop over months of disuse. Alternatively, the expansion vessel may have lost its charge. Always check the gauge before running your heating test.
What should I do if my TRV pin won’t unstick? If gently tapping or pressing the metal pin does not release it, the valve is permanently seized internally. The entire valve will need to be drained and replaced by a plumber.
Is a humming noise normal when I turn the heating on? A quiet hum is normal. It’s just the circulating pump running steadily. Grinding, rattling or struggling noises are different, and usually point to magnetite sludge restricting the pump, which may need a powerflush to clear.
