No Hot Water But Heating Works - What to Check for Your Ashton-under-Lyne Boiler

Published October 2026 | Boiler Repair

There's a particular type of frustration that comes with turning on a hot tap and getting nothing but cold water - especially when you can feel that the radiators are perfectly warm. It's one of the most common calls our engineers receive from homeowners across Ashton-under-Lyne, and the good news is that the cause is usually identifiable and fixable. The better news is that understanding why it happens puts you in a much stronger position to prevent it coming back.

This guide covers what to check when you have heat but no hot water, why that fault develops, and the maintenance habits that stop it becoming a recurring problem. We'll also look at the bigger picture: how long your boiler should realistically last, what a proper annual service involves, and how to know when repair stops making sense.

How Long Should a Boiler Last and What Affects That

Most modern gas boilers are designed to last around 10 to 15 years. That's the figure manufacturers commonly cite, and it broadly matches what our engineers observe in practice across properties in Ashton-under-Lyne. But that range hides a lot of variation. Some boilers fail inside five years through poor installation or neglect. Others push well past 20 years because they've been looked after from the start.

Several factors determine which end of that range your boiler ends up on.

Installation quality is the first and arguably the most important factor. A boiler that was undersized for the property, incorrectly commissioned, or connected to pipework full of debris will work harder than it should from day one. That accumulated stress adds up. Worcester Bosch and Vaillant units that are properly installed and serviced regularly tend to outlast cheaper alternatives that were fitted poorly.

Water quality matters more than most people realise. Greater Manchester has moderately hard water in many areas, and limescale is one of the most consistent enemies of boiler longevity. It builds up inside the heat exchanger, forces the boiler to work harder to transfer heat, and contributes directly to faults like intermittent hot water. Adding a scale reducer or magnetic filter at installation - and keeping it maintained - makes a measurable difference over the boiler's lifetime.

Usage patterns play a role too. A boiler in a household of six people that runs constantly through winter is under far more stress than one heating a two-person flat. Combi boilers in busy households are particularly vulnerable because they switch between heating and hot water modes frequently, putting more wear on the diverter valve - the component most commonly responsible when your heating works but hot water doesn't.

Servicing history is perhaps the most controllable factor. A boiler that has received annual Gas Safe maintenance since installation is in a fundamentally different condition from one that hasn't been touched in five years. The service record also affects warranty validity and the resale value of the property.

The Maintenance That Actually Makes a Difference

When heating is working but hot water has stopped, the underlying cause is almost always something that developed gradually rather than a sudden catastrophic failure. That's why maintenance matters - it catches the progression of a fault before it becomes a breakdown.

Annual Gas Safe service is non-negotiable. Only a Gas Safe registered engineer is legally permitted to work on gas appliances in the UK, and an annual service is where most developing problems get caught. A good service finds a sticking diverter valve before it fails completely, catches corrosion early, and keeps the heat exchanger clean. Budget typically between 70 and 120 pounds for a service from a reputable engineer in the Greater Manchester area.

Magnetic system filter maintenance - a Magnaclean or equivalent filter protects the boiler from the black iron oxide sludge (magnetite) that builds up in heating systems over time. The filter needs cleaning annually, usually as part of the service. If your system doesn't have one fitted, ask your engineer about adding one.

System inhibitor topping up - the chemical inhibitor in your central heating water prevents internal corrosion and sludge formation. It breaks down over time and needs replenishing, typically every one to two years.

Power flushing - if your system has significant sludge buildup, a power flush forces high-velocity water and chemicals through the pipework to clear it. This is typically needed every five to eight years in older systems, or when a new boiler is installed on an existing circuit. Costs commonly fall between 400 and 800 pounds depending on the number of radiators and the condition of the system.

Pressure checks - a combi boiler should typically sit between 1.0 and 1.5 bar when cold. If the pressure drops regularly, there's a leak somewhere in the system. If it rises beyond 2.5 bar, the expansion vessel may need attention. Neither should be left unchecked.

Our engineers use the Voltrade GoFIX diagnostic tool to run a systematic check across all these parameters when visiting properties in Ashton-under-Lyne, which helps identify the root cause of a fault rather than just the symptom that triggered the call.

Why Heating Works But Hot Water Doesn't - the Checks to Run First

The most frequent cause in combi boilers is a faulty or sticking diverter valve. In a combi, one heat exchanger handles both central heating and domestic hot water. The diverter valve switches between the two modes depending on demand. When it sticks in the heating position - or partially seizes - the boiler happily heats the radiators but can't redirect flow to the hot water circuit. The fix usually involves replacing the valve, which costs between 150 and 300 pounds including parts and labour.

Before calling an engineer, there are a few checks worth running yourself.

1. Check your programmer and timer settings. A power cut or battery failure can reset the clock on your programmer, putting your hot water on a schedule that doesn't include right now. Check the time displayed is correct and that the hot water programme is set as expected.

2. Check the boiler pressure gauge. Low pressure (below 1 bar) can cause a combi boiler to run heating but fail on hot water. If the gauge reads below 1 bar, you may be able to repressurise via the filling loop - your boiler manual will walk you through this. If you're not comfortable doing it, an engineer can do it quickly and cheaply.

3. Look for an error code on the display. Modern boilers from Worcester Bosch, Ideal, and Baxi typically show a fault code when something's wrong. Note it down - it tells the engineer a great deal before they've even looked at the unit.

4. For system or heat-only boilers with a hot water cylinder - the fault is more likely in the motorised zone valve or the cylinder thermostat. Check that the cylinder thermostat is set to around 60 degrees Celsius. Listen for whether the motorised valve on the pipework near the cylinder is making a noise when hot water is called for.

5. Check the hot tap flow rate carefully. If you're getting some warm water but it's not reaching temperature, the problem may be a failing thermistor (temperature sensor) rather than a complete diverter failure - a different and typically cheaper repair.

Warning Signs Your Boiler Is Reaching End of Life

The no-hot-water fault is sometimes a one-off repair in an otherwise healthy boiler. Other times it's one symptom in a pattern that points toward end of life. Knowing the difference saves you from spending money on repairs that are only buying time.

Increasing frequency of breakdowns. One repair every few years is within normal range. Two or three different faults in a single heating season is a different situation entirely. Parts in older boilers tend to fail in sequence as they approach the end of their design life.

Noticeably rising energy bills. An ageing boiler loses efficiency as heat exchangers scale up and components wear. If your gas bills have been climbing without a corresponding change in usage habits, the boiler may be working harder for the same output.

Unusual noises. Kettling (a rumbling or boiling sound) indicates limescale on the heat exchanger. Banging or clunking on startup can suggest pump wear or expansion issues. These don't always mean the boiler is dying, but they're worth getting checked promptly rather than ignored.

Yellow or orange flame. A gas boiler's burner should produce a crisp blue flame. A yellow or orange tinge indicates incomplete combustion and is a potential carbon monoxide risk. This is a call-the-engineer-today situation, not a wait-and-see one.

Parts availability. For boilers over 12 to 15 years old, spare parts can become difficult or expensive to source. Our engineers working across the Greater Manchester area increasingly find that older Potterton and Baxi models from the early 2010s are at the point where parts are no longer cost-effective to track down.

Repair vs Replace - the Honest Calculation

The repair-or-replace decision comes up whenever a significant fault is diagnosed, and it's one where a good engineer should give you a clear steer rather than simply quoting for the job in front of them.

A useful rule of thumb is to compare the repair cost against the boiler's age multiplied by roughly 50 to 60 pounds per year. For a 12-year-old boiler, think carefully about any repair over 600 to 720 pounds. It's not a hard rule, but it provides a framework for the decision.

Common repair costs for faults that cause the heating-but-no-hot-water problem typically look like this.

Diverter valve replacement - typically between 150 and 300 pounds including parts and labour. A worthwhile repair on a younger, otherwise healthy boiler.

Motorised zone valve - commonly between 100 and 250 pounds. Usually a sensible repair at most boiler ages.

Cylinder thermostat or thermistor - typically 80 to 200 pounds. A minor repair that's almost always worth doing.

Heat exchanger replacement - commonly 300 to 600 pounds or more. This is where the age calculation really matters, because a heat exchanger failure on a 14-year-old boiler is often a clear signal to replace rather than repair. For Ashton-under-Lyne homeowners considering a full replacement, a new A-rated combi boiler typically costs between 1,800 and 3,500 pounds supplied and fitted, depending on size and complexity.

Annual Service - What It Should Include

An annual boiler service isn't just about ticking a warranty box. Done properly, it's the single most effective tool for extending boiler life and catching faults before they become emergencies.

Here's what a thorough Gas Safe service should cover.

1. Visual inspection of the boiler casing, flue, and pipework for signs of corrosion, damage, or leaks.

2. Burner inspection and cleaning - the burner is removed, checked for wear, and cleaned of any debris or residue.

3. Flue gas analysis - a combustion analyser is connected to confirm the boiler is burning gas efficiently and safely. This is a critical safety check, not an optional extra.

4. Heat exchanger check - inspected for scaling, cracking, or structural damage.

5. Controls testing - thermostat, programmer, and all safety devices are tested for correct operation, including the diverter valve where applicable.

6. Pressure and expansion vessel check - system pressure and expansion vessel pre-charge are verified and corrected if needed.

7. Magnetic filter service - if fitted, the filter is cleaned and inhibitor levels checked.

8. Gas tightness check - the engineer confirms there are no gas leaks at the appliance connections.

What a service should not be is a 20-minute visit where the engineer glances at the boiler and prints you a certificate. If it feels rushed, ask specifically which checks were carried out. A legitimate Gas Safe engineer will have no hesitation explaining what they did.

Simple Habits That Extend Your Boiler's Life by Years

Beyond the annual service, there are everyday habits that make a real difference to how long your boiler lasts and how reliably it performs between services.

Keep the boiler ticking over in mild weather. Turning the boiler off completely for months at a time means seals dry out and the diverter valve can stick in position - which is exactly the fault that causes you to lose hot water. Setting the heating to a low background temperature, even 12 to 15 degrees through spring and autumn, keeps everything moving.

Check the pressure monthly. It takes 30 seconds. If it's dropping consistently, there's a small leak somewhere that's cheaper to find and fix early than after it's caused months of quiet corrosion.

Bleed radiators once a year. Air in the system forces the pump to work harder and reduces efficiency across the whole circuit. Bleeding takes a few minutes per radiator and costs nothing but a small amount of water.

Don't ignore small leaks. A dripping valve or weeping joint might seem trivial, but it slowly drops the system pressure, allows air ingress, and can cause localised corrosion that spreads. Small leaks dealt with promptly rarely become big ones.

Make sure the flue is unobstructed. Boiler flues can get blocked by debris, bird nests, or ice during severe frost. A blocked flue triggers the boiler's safety lockout. Check it's clear after any severe weather, particularly in exposed locations.

Know where your isolation valves are. If something does go wrong, being able to shut off the gas or water supply quickly limits the damage. Make sure everyone in the household knows where the main gas isolation valve is located, and that it actually turns freely if it hasn't been touched in years.

For Ashton-under-Lyne homes with older pipe runs or properties that have had several different boilers over the years, it's also worth asking your engineer whether the system pipework is correctly configured for the current unit. Mismatched pipe sizing or incorrectly set bypass valves put unnecessary strain on the boiler that compounds over time.

Maintenance Questions

Why does my combi boiler heat the radiators but not the hot water?

In most cases this points to a sticking or failed diverter valve. This component is responsible for directing the boiler's output between the central heating circuit and the domestic hot water circuit. When it sticks in the heating position, radiators stay warm but taps run cold. A Gas Safe engineer can confirm the diagnosis and typically replace the valve in a single visit, with costs commonly falling between 150 and 300 pounds for parts and labour combined.

How often should I have my boiler serviced in Ashton-under-Lyne?

Every 12 months, without exception. Annual servicing is the minimum recommended by manufacturers, is required to maintain most boiler warranties, and is the only reliable way to catch developing faults before they become expensive breakdowns. In Greater Manchester's moderately hard water areas, the annual service is also the right time to check for limescale accumulation in the heat exchanger and confirm that system inhibitor levels are adequate for the water chemistry.

Can I fix a boiler fault myself if I know what the problem is?

How do I know if my boiler needs replacing rather than repairing?

The main indicators are age combined with repair cost. If your boiler is over 12 years old and you're looking at a repair bill above 500 to 600 pounds, replacement often makes more financial sense - particularly given the efficiency gains a modern A-rated unit delivers over time. Multiple faults within a single year, persistent leaks, or the unavailability of spare parts are also strong signals that the boiler has reached the end of its practical working life.