Heating Not Working in Winter? Why the Problem Often Starts in Summer (Mid Sussex)

Terry Matthews
Jul 10, 2025
7 min read

Updated: Jan 11

Terry Matthews from Smart Heat Experts, showing you how to save hundreds — Turning on the heating during the summer months, just for 5 minutes, could save you hundreds.

If your heating has packed up the moment the cold weather hits, you are not alone. We see it every year across Haywards Heath, Burgess Hill, Hassocks, Ardingly and Cuckfield.

That familiar November moment when the chill hits and nothing happens. Radiators stay stone cold, the boiler clicks, and you are suddenly searching for emergency help.

Here’s the surprising bit though. A lot of winter heating breakdowns start in summer, when systems sit quietly for months and key moving parts do not move at all.

This guide covers two things:

What to do if your heating is not working right now
A simple 5 minute summer habit that can prevent common winter failures

Writer: Terry Matthews, Smart Heat Experts Ltd

Areas covered: Haywards Heath and Mid Sussex, including Burgess Hill, Hassocks, Ardingly, Cuckfield and nearby villages.

Quick answer

If your heating is not working in winter, the most common causes are low system pressure, frozen condensate, controls not calling for heat, stuck valves, or a boiler safety lockout. Start with safe checks like thermostat settings and boiler pressure. If you have repeated lockouts, a visible leak, or pressure keeps dropping, stop and book a professional. For prevention, run your heating for five minutes once a month through summer to keep valves, pumps, and diverters moving.

“My heating doesn’t come on even though the thermostat says it should.”“Our radiators won’t warm up but we’ve got hot water.”“Why does the heating always break when it’s cold?”

These are real quotes from real customers. The root cause? Lack of movement and regular use.

If your heating is not working in winter right now, check these first

Step 1: Check your thermostat and programmer

Broken thermostat haywards heath west sussex

Before anything else, confirm your controls are actually calling for heat.

What to check:

Is the thermostat set higher than the current room temperature?
Is the programmer set to heating on, not off, holiday mode, or timed out?
If it is a wireless thermostat, have the batteries been changed recently?
If you have zones (upstairs and downstairs), is the right zone calling?

Common local scenario: One zone works, the other does not.

This often points to a zone valve or actuator issue rather than a boiler fault.

Step 2: Check boiler pressure

Boiler pressure low in Haywards Heath West Sussex

Low pressure is one of the most common reasons a boiler will stop heating.

Most systems like to sit around 1.0 to 1.5 bar when cold. If it is significantly lower, the boiler may lock out.

What to do:

Look at the pressure gauge or digital display on the boiler
If pressure is below the minimum, topping up may restore heating

Important:Only top up if you know how and you can do it safely. If you are unsure, stop and call us. Overfilling can cause other issues.

Step 3: Check for frozen condensate pipe

In cold snaps across Mid Sussex, frozen condensate pipes are a regular issue on condensing boilers.

Signs of a frozen condensate:

Boiler shows a fault code
Boiler tries to start then shuts down
Heating works intermittently during the day but fails overnight

What you can safely look for:

External white plastic pipe (usually 21.5mm on older installations, with 32mm now recommended where possible to reduce freezing risk)
Ice around the pipe or at the outlet

If you suspect a frozen condensate, do not start dismantling anything if you are not confident. We can talk you through safe steps, and if needed we can attend.

Step 4: Are you getting hot water but no heating?

This is a key clue.

If you have hot water but radiators are cold, common causes include:

A stuck diverter valve inside a combi boiler
A stuck motorised zone valve on a system boiler
Control fault where heating demand is not being sent

This is exactly where the “summer inactivity” problem often shows up, because the diverter or zone valve might not have moved properly for months.

Visible boiler leak under cupboard, book an engineer.

Step 5: Listen and look for obvious warning signs

Do a quick safety and common sense check.

Look for:

Any water marks, drips, or staining near the boiler or pipework
Unusual noises (loud banging, grinding, squealing)
Repeated lockouts or reset cycles

If you can see water leaking, stop and call. A small drip can quickly become damage.

When to stop and call a heating engineer

Some situations should not be messed with.

Call for help if:

You smell gas or suspect a gas leak
The boiler keeps locking out after resetting
Boiler pressure keeps dropping after topping up
You can see water leaking from the boiler, PRV discharge, or heating pipework
Radiators stay cold even though the boiler is firing
You are unsure and do not want to risk making it worse

If you are in Haywards Heath, Burgess Hill, Hassocks, Ardingly, Cuckfield or nearby, you can call Smart Heat Experts and we will advise you properly.

Submit your issue here for a fast quote

Why heating not working in winter often starts in summer

The real reason: systems sit dormant and parts stop moving

Heating systems have moving components that rely on regular movement to stay reliable. When they sit unused through summer, parts can stiffen, stick, or fail to activate when winter demand hits.

This is why customers often say things like:

“My heating doesn’t come on even though the thermostat says it should.”
“Our radiators won’t warm up but we’ve got hot water.”
“Why does the heating always break when it’s cold?”

In many cases, the root cause is not the cold weather itself. It is months of inactivity, then suddenly asking everything to run full time.

Submit your issue here for a fast quote

Common culprits caused by inactivity

Motorised zone valves and actuator heads

If you have separate heating zones, these valves open and close to let heat flow where it is needed. When they do not move for months, they can stick

hot water is working but heating is no longer working

Diverter valves inside combi boilers

Combi boilers switch between hot water and heating using a diverter valve. In summer, many homes use hot water daily but rarely use heating mode, so the diverter may not exercise properly.

Secondary pumps for zoned systems

Pumps can seize or struggle to start after long periods of inactivity, especially if system water quality is poor or the system is older.

They are commonly found in airing cupboards on traditional systems, or within the boiler casing on combi and some system boilers.

Thermostats and programmers that have not been used for months

Over the past 15 years, many heating controls have become wireless or partially wireless, often running on low voltage batteries. This can catch people out.

The confusing part is that the control can still look like it’s on.

The screen lights up, the schedule looks normal, but the batteries are actually flat or on their way out.

The signal to the boiler or valves is weak or failing altogether.

We see this far more often than people realise. In 2024 alone, we attended 11 call outs that were purely down to low batteries in heating controls. In 2025, that number jumped to 34.

No boiler fault. No failed parts. Just batteries.

It’s a simple thing, but when controls sit unused over summer, batteries drain quietly.

When winter arrives and the heating is finally needed, the system doesn’t respond as it should.

Swapping batteries once a year, ideally before winter, can save a lot of frustration and an unnecessary call out.

The 5 minute summer habit that could save you hundreds

Turn your heating on for five minutes once a month in summer

Here is the preventative tip we recommend to homeowners across Mid Sussex.

Once a month, during summer, turn your heating on for five minutes.

No tools. No apps. Just a quick routine that keeps everything moving.

Step by step

Step 1: Choose a day each month

Pick something easy to remember, like the first Saturday of the month.

Step 2: Raise the thermostat a few degrees

Raise it 2 to 3°C above the current room temperature.

Example: if the house is at 18°C, set it to 21°C.

Step 3: Let it run for five minutes

You are not trying to heat the whole home. You are simply exercising the system.

Step 4: Turn it back down again

After five minutes, return your thermostat to normal.

That’s it.

What this does behind the scenes

Running heating mode briefly:

activates the boiler heating circuit
triggers zone valves and opens actuator heads
spins pumps and circulates water
moves diverter valves inside combi boilers
helps prevent components sticking when you need them most

5 minute summer heating check list haywards heath

What zones should you activate?

To get the benefit, include everything that is part of your heating system:

all room thermostats (upstairs, downstairs, extensions)
towel rails on heating circuits
any underfloor heating zones
combi boiler heating mode, even if hot water works daily

A lot of combi boilers only move the diverter valve properly when switching into heating. If that pin does not move for months, it can jam. The result is hot water working, but radiators staying cold.

Why issues sometimes show up when you test the heating

Homeowners sometimes worry that turning the heating on in summer will “cause” a fault.

It does not create faults out of thin air, but it can reveal issues that were already there, just hidden.

Common examples

PRV discharge outside, dripping after heating is used

If pressure rises too high when heating runs, the pressure relief valve may lift. Sometimes a PRV that has lifted can then fail to reseal perfectly if there is debris or scale.

Expansion vessel problems

If the expansion vessel charge is low, heating pressure can climb rapidly when the system warms up. This can lead to nuisance pressure issues and sometimes PRV discharge.

Sticking valves or lazy pumps

A valve or pump that is borderline may work once or twice then struggle. Catching that in summer is far better than discovering it on the coldest week of the year.

Why summer is the best time to catch these

better availability for bookings & Servicing
less stress and no emergency rush
often cheaper to address early, before secondary damage happens

Summer heating health checklist

Use this once a month between May and September:

raise thermostats 2 to 3°C above room temperature
let the boiler fire up for 5 minutes
check all zones activate
include towel rails and underfloor heating
combi boiler: turn heating on to move the diverter valve
if anything does not respond, get it checked early

Final word from Smart Heat Experts

We do this routine ourselves. Every zone, towel rail and loop gets a quick run through summer, because it helps prevent the exact breakdowns we see every winter.

If you have never done this before, now is a great time to start. It is quick, simple, and can save you the stress of a winter callout or a stuck valve when you need heat the most.

If your heating is playing up, or you want your boiler serviced before winter hits, we are local and we are here to help.