No Hot Water But Heating Works - What to Check in Your Banbury Home

Published October 2026 | Boiler Repair

A homeowner in Banbury wakes up on a cold Tuesday morning, pads downstairs, and turns on the kitchen tap. They wait. The water runs cold, then cooler still. They check the radiators in the hallway - warm to the touch, working perfectly. The boiler is firing, the pressure gauge is reading normal, and there's no error code flashing on the display. Everything looks fine. But there's no hot water.

This particular scenario - heating working, hot water absent - is one of the most common boiler-related calls our engineers attend across Banbury and the wider Oxfordshire area. It's confusing precisely because the system seems to be doing something right. The fault, though, is almost always traceable to one or two specific components, and knowing what to look for can save you time, money, and an unnecessary wait in the cold.

What Was Actually Going On

In this case, the homeowner had a combi boiler - a Worcester Bosch Greenstar installed about nine years earlier. Combi boilers handle both central heating and domestic hot water from a single unit, and they do so by switching between the two demands using a component called a diverter valve.

The diverter valve is essentially a mechanical gate. When you turn on a hot tap, it's supposed to close off the heating circuit and redirect the boiler's heat energy toward producing hot water. When there's a call for heating instead - from your thermostat or programmer - it routes energy back to the radiators. On a healthy boiler, this switching happens smoothly and constantly throughout the day.

What our engineer found was that the diverter valve had partially seized in the heating position. It could still move enough to let the boiler fire for central heating, but it wasn't fully redirecting flow when a hot tap was opened. The result was exactly what the homeowner experienced: radiators got warm, but the hot water circuit was being starved. As BOYLA's guide to this fault explains, a stuck or failing diverter valve is one of the most common causes of this specific symptom pattern on combi boilers.

This is worth understanding clearly. If you have a combi boiler and your heating works but your hot water doesn't, the diverter valve is typically the first thing a Gas Safe engineer will check. It's not always the culprit - but it's the most likely one.

What About System and Conventional Boilers?

Not every home in Banbury runs on a combi boiler. Older properties - and there are plenty of them across Oxfordshire - often have a system boiler paired with a hot water cylinder, or a conventional (heat-only) boiler with both a cylinder and a cold water tank in the loft.

On these setups, the symptom of heating-works-but-no-hot-water points to a different set of components. The most common causes include:

• A faulty motorised valve (also called a zone valve or mid-position valve) that's stuck on the heating circuit
• A cylinder thermostat that's failed or been set incorrectly
• An immersion heater element that's burned out
• A wiring fault between the programmer and the hot water circuit
• A failed pump that isn't circulating water to the cylinder

In the case of a system or conventional boiler, the heating and hot water circuits are more physically separate, which is why one can fail without affecting the other. Homebuilding's overview of this fault covers how the symptom pattern shifts depending on your boiler type - it's a useful reference if you're unsure what system you have.

How the Problem Was Resolved

For the Banbury homeowner with the Worcester Bosch combi, the resolution was a diverter valve replacement. This is a job that must be carried out by a Gas Safe registered engineer - it involves accessing internal boiler components and, on most models, draining part of the system. Gas Safe registration isn't a preference; it's a legal requirement for any work on gas appliances in the UK.

Our engineer isolated the boiler, drained the necessary section of the system, removed the old valve assembly, fitted the replacement part, and refilled and repressurised the system. The whole job took around two hours on-site. On some boiler models, access is tight and the job takes longer; on others, the valve is easier to reach and the work moves quickly.

After the repair, the engineer ran a full function test - checking hot water temperature at multiple outlets, confirming the heating circuit was still responding correctly, and verifying that the boiler was switching cleanly between the two modes. A quick check with the Voltrade GoFIX diagnostic tool confirmed there were no underlying fault codes or secondary issues that had been masked by the primary fault.

What If It's a Cylinder System?

For homes with a hot water cylinder, the fix depends on where the fault sits. A stuck motorised valve can sometimes be freed by manually operating it (there's usually a manual lever on the valve body), though this is a temporary workaround rather than a repair. A failed cylinder thermostat is a relatively low-cost fix. An immersion heater element replacement is more involved but still within the scope of a standard engineer visit.

What matters is getting the right diagnosis first. Replacing parts speculatively is expensive and doesn't always work. A proper diagnostic - testing the cylinder thermostat, checking the valve's electrical supply, and confirming the programmer is sending the right signals - takes maybe 20 to 30 minutes and prevents unnecessary part swaps.

What This Cost and How Long It Took

Diverter valve replacement on a combi boiler typically costs between 180 and 350 pounds in total, including parts and labour. The part itself varies in price depending on the boiler brand and model - Worcester Bosch, Vaillant, Ideal, and Baxi all use different components, and some proprietary parts carry a premium. If your boiler is older or out of warranty, check that the part is still available before committing to a repair.

Labour for this type of job in Banbury and across Oxfordshire typically runs at 70 to 120 pounds per hour, with most repairs taking one to two hours. Some engineers charge a fixed call-out fee on top; others include the first hour in a flat rate. Always confirm the pricing structure before the engineer starts work.

For cylinder-related faults, costs vary more widely. A motorised valve replacement typically falls between 120 and 220 pounds. A cylinder thermostat is cheaper to fix - often 80 to 150 pounds all in. An immersion heater element replacement usually sits between 100 and 180 pounds, depending on the element type and access. Plumbing Correct's breakdown of the nine most common causes gives a useful cost-by-fault overview if you want to cross-reference before booking an engineer.

The Banbury homeowner had their hot water back by early afternoon - a same-day resolution from a fault that, to them, had seemed mysterious. The total bill came in at 265 pounds, which sits comfortably within the typical range for a diverter valve repair on a boiler of that age and brand.

How to Spot the Same Issue in Your Home

Before calling anyone out, there are a few checks worth doing yourself. None of them require tools or technical knowledge, and they can sometimes point you to a fix that costs nothing.

1. Check the boiler pressure. On most combi boilers, the pressure gauge should read between 1 and 1.5 bar when the system is cold. If it's below 0.5 bar, the boiler may not fire properly for hot water even if it still manages to heat the system. Topping up the pressure via the filling loop (a small braided hose under or near the boiler) is something most homeowners can do safely - check your boiler's manual for the specific procedure.
2. Check the programmer and thermostat settings. It sounds basic, but it's worth confirming that the hot water schedule on your programmer is set correctly. A common cause of "no hot water" is simply a timer that's been accidentally changed - particularly after a power cut, which can reset some models to factory settings.
3. Run the tap for longer than you'd expect. If the diverter valve is sluggish rather than fully seized, you may get a trickle of hot water after a prolonged wait. This is a sign the valve is failing rather than failed - and it's worth acting on before it stops working entirely.
4. Check for error codes. Modern boilers display fault codes when something's wrong. Look up your boiler's model number and the displayed code - the manufacturer's website will usually tell you what it means. Not all faults show a code, but many do.
5. Feel the cylinder (if you have one). If your home has a hot water cylinder, touch the upper section carefully. If it's cold when it should be hot, the fault is likely in the hot water circuit rather than the boiler itself - a motorised valve, thermostat, or immersion heater is the likely culprit.

If none of these checks reveal an obvious cause, or if the cause is clear but involves gas components, stop there and call a Gas Safe registered engineer. Attempting to dismantle or adjust gas components without the correct registration is both dangerous and illegal in the UK.

Lessons - What Every Banbury Homeowner Should Know

The most important lesson from this type of fault is that "heating works" and "the boiler is fine" are not the same statement. A combi boiler can be firing, maintaining pressure, and keeping your radiators warm while simultaneously failing at its second job - producing hot water. The two functions share components, but they also have dedicated parts, and those parts fail independently.

In Banbury, as in much of Oxfordshire, the housing stock is a mix of ages and boiler types. Victorian and Edwardian terraces in the town centre tend to have older systems - sometimes converted from gravity-fed conventional setups to system boilers, sometimes still running the original cylinder arrangement. More recently built estates typically have combis. Knowing which type of system you have is the first step to diagnosing any fault efficiently.

Diverter valve failure is particularly common on combi boilers that are over eight years old. The valve contains rubber seals and a mechanical actuator that wear with use. If your boiler is in this age bracket, it's worth being aware that the diverter valve may need attention in the coming years - and if you notice the hot water becoming inconsistent or slow to arrive before it stops entirely, that's the time to get it looked at. Catching a valve that's starting to stick is cheaper than replacing one that's fully failed.

For cylinder systems, the cylinder thermostat and motorised valve are the equivalent weak points. Thermostats can drift out of calibration over time, and motorised valves have a mechanical lifespan measured in the tens of thousands of operations - eventually, they wear out. Having an annual service that checks these components is the most reliable way to catch failures before they leave you without hot water.

Annual boiler servicing is not just good practice in Banbury - it's particularly important in areas with older housing stock where systems may have been modified or extended over the years. A Gas Safe registered engineer carrying out a service will check the heat exchanger, flue, seals, and key components including the diverter valve or cylinder controls. The service won't prevent every fault, but it significantly reduces the likelihood of unexpected breakdowns.

One final point: if an engineer quotes for a repair on a boiler that's over 12 to 15 years old, it's worth asking them whether a repair makes financial sense compared to a replacement. Parts for older boilers can be expensive, and if the diverter valve has failed, other wear-related components may not be far behind. A good engineer will give you that comparison without pushing you toward the more expensive option.

Related Questions

Can I have hot water without a working boiler?

Yes, if your home has a hot water cylinder with an immersion heater. The immersion heater is an electric element inside the cylinder that can heat water independently of the boiler. If your boiler has broken down completely, switching on the immersion heater is a useful short-term workaround while you wait for a repair. Check your airing cupboard for the immersion switch - it typically looks like a standard light switch on the wall near the cylinder.

Why does my boiler fire when the hot tap is turned on but the water stays cold?

This is a classic sign of a diverter valve fault on a combi boiler. The boiler responds to the demand signal and fires, but the valve isn't redirecting flow to the hot water circuit correctly. The heat generated goes into the heating system instead of the domestic water. You'll often hear the boiler working but feel no heat at the tap. This needs a Gas Safe engineer to diagnose and repair - it won't resolve itself.

How long does a diverter valve repair take in Banbury?

Most diverter valve replacements take between one and two hours on-site, depending on the boiler model and how easy the valve is to access. Some older Worcester Bosch and Vaillant models require more disassembly than others. Same-day appointments are commonly available in Banbury for urgent no-hot-water calls, particularly during weekdays. Always check that the engineer is Gas Safe registered before booking.