No Hot Water But Heating Works in Barnstaple - What to Check

Published October 2026 | Boiler Repair

It's a damp autumn morning in Barnstaple, the radiators have been ticking away for an hour and the living room is warm - but every tap in the house is running cold. The boiler hasn't locked out, there's no flashing error code, and everything looks normal from the outside. This is one of the most common faults our engineers see across Devon, and understanding why it happens can save you both time and money before you pick up the phone.

Understanding the Problem - What Is Actually Happening

When your heating works but hot water doesn't, it tells you something specific about where the fault lies. Your boiler is clearly firing and producing heat - that part is working. The problem is almost always in how that heat gets directed to the hot water side of the system, or in the individual components that control your hot water supply.

Central heating and domestic hot water use different pathways through your system. In a combi boiler - which is common in Barnstaple homes - a component called the diverter valve is responsible for switching flow between the two circuits. In a system with a hot water cylinder, motorised valves and a cylinder thermostat control when hot water gets heated. When one of these components fails, you can end up with heating working perfectly while hot water is completely absent.

The fault is rarely the boiler itself failing outright. More commonly, it's a single mechanical or electronic component that has worn out or got stuck. That's why this type of fault is usually repairable without a full boiler replacement - good news for your wallet.

The Most Common Causes

Our engineers see a predictable set of causes for this problem. Here are the ones worth knowing about, roughly in order of how often we encounter them.

A Faulty Diverter Valve

If you have a combi boiler - brands like Worcester Bosch, Vaillant, Ideal, or Baxi are all common in Devon - the diverter valve is the most likely culprit. This valve is a small mechanical component that redirects hot water from your heating circuit to your taps when you open them. Over time, the valve can get stuck in the heating position, which means the boiler keeps warming your radiators but never switches over to heat your domestic hot water.

A diverter valve stuck in the heating position is sometimes intermittent at first. You might get a brief burst of lukewarm water before it runs cold, or the hot water might work fine in the morning but fail by the evening. Plumbing specialists identify this as one of the most likely causes of this specific fault pattern. Diverter valve replacement typically costs between 150 and 350 pounds depending on the boiler model, and is a job that must be done by a Gas Safe registered engineer.

A Faulty or Stuck Motorised Valve

In homes with a separate hot water cylinder - often found in older Barnstaple properties - the heating and hot water circuits each have their own motorised zone valve. These valves are electrically operated and can fail in two ways: they can jam shut (cutting off hot water completely) or jam open (meaning the system can't properly prioritise one circuit over the other).

A failed motorised valve sometimes makes its presence known audibly - you might hear a clicking or buzzing near the valve head when the system calls for hot water. In some cases the actuator head fails while the valve body is fine, which makes replacement relatively simple and inexpensive - typically 80 to 150 pounds for parts and labour.

Low Boiler Pressure

This is one you can check yourself without any technical knowledge. Most combi boilers have a pressure gauge visible on the front panel - it should read between 1 and 1.5 bar when the system is cold. If it's below 0.5 bar, low pressure can affect the boiler's ability to heat water for the taps, even while the heating manages to keep running.

Topping up boiler pressure is done via a filling loop - a small braided hose connection, often underneath the boiler. Your boiler's manual will walk you through this, and it's one of the few things you can manage yourself. If the pressure drops again within days or weeks, that suggests a leak somewhere in the system and you'll need an engineer to track it down.

A Faulty Thermistor or Temperature Sensor

Boilers use thermistors - small temperature sensors - to monitor water temperature on both the heating and hot water circuits. If the hot water thermistor gives a false reading, the boiler may assume the water is already hot enough and never fire up to heat it. Boiler specialists confirm that sensor faults are a recognised cause of this type of selective failure.

This fault won't always trigger an obvious error code on older boilers, though modern boilers often display a fault code that an engineer can cross-reference with the manufacturer's data. Thermistor replacement is a relatively low-cost repair - commonly between 80 and 200 pounds including parts and labour.

Problems with the Hot Water Cylinder

If your Barnstaple home has a hot water cylinder, the issue might be with the cylinder rather than the boiler. The immersion heater element could have failed, or the cylinder thermostat might have packed in or been set too low. Check that the cylinder thermostat is set to around 60 degrees Celsius - any lower and the water may not feel hot enough at the tap, and you also risk legionella bacteria growth if it drops below 55 degrees.

A failed immersion heater element is a standard replacement job for a qualified electrician. If the primary heating coil inside the cylinder has failed, that's a more involved repair. Heating engineers typically check both the cylinder thermostat and the immersion heater as part of a diagnostic visit for this type of fault.

A Programmer or Timer Fault

Your heating programmer or smart thermostat controls when each circuit runs. It's possible that the hot water schedule has been accidentally switched off, or the programmer itself has developed a fault that affects only the hot water zone. Before calling anyone, check your programmer settings and make sure the hot water is set to come on at the right times. This is especially worth checking after a power cut, as some older programmers reset to factory defaults and can lose their hot water schedule entirely.

Solutions That Actually Work

Work through these checks in order before booking an engineer. They're all safe to do yourself and they cover the most common causes.

1. Check your boiler pressure. Look at the pressure gauge on the front of the boiler. It should be between 1 and 1.5 bar when cold. If it's low, use the filling loop following your boiler manual's instructions to bring it back up.
2. Check your programmer settings. Make sure the hot water is scheduled to run, and that it hasn't been accidentally set to "off" or reset to a default programme. Check for any zone settings that might have the hot water disabled.
3. Check the cylinder thermostat if you have a cylinder. Make sure it's set to around 60 degrees and hasn't been knocked down.
4. Look for an error code on the boiler display. Modern boilers display fault codes when something goes wrong. Note the code down and look it up in your manual - it often points directly to the failed component.
5. Run the Voltrade GoFIX diagnostic check. Our GoFIX tool helps you identify what's likely wrong before an engineer visits, so you go into the appointment with a clearer picture of the fault - and potentially a faster, cheaper fix.
6. Try a boiler reset. Hold the reset button on your boiler for a few seconds. Some boilers will clear a temporary fault and restore normal operation. If it works but the problem returns within a day or two, there's an underlying issue that needs a professional to investigate.

If none of the above resolves the problem, you're looking at a component fault that needs a Gas Safe registered engineer. Don't try to go further than these checks yourself.

When You Need Professional Help vs Sorting It Yourself

There's a clear dividing line here. Checking boiler pressure, adjusting programmer settings, and resetting the boiler are all things a homeowner can do safely. Everything else - replacing a diverter valve, servicing a motorised valve, testing thermistors, or working on any gas components - requires a Gas Safe registered engineer by law. This isn't just a precaution: working on a gas appliance without Gas Safe registration is illegal in the UK and carries serious safety risks for you and your household.

Our advice for Barnstaple homeowners is to work through the self-check steps above, then book an engineer if the fault persists. Don't attempt to disassemble the boiler or interfere with any gas connections yourself. It can also invalidate your boiler's manufacturer warranty, which makes an already annoying situation significantly more expensive.

If your boiler is more than 12 to 15 years old, it's also worth having a broader conversation with the engineer about whether repair or replacement makes more sense economically. Older boilers can develop multiple component failures in quick succession, and a repair costing 250 to 400 pounds on an ageing unit may not represent the best value when weighed against the cost and efficiency gains of a modern replacement.

What to Expect from a Repair Visit

When a Gas Safe engineer visits your Barnstaple home to investigate a no-hot-water fault, the visit typically follows a clear pattern.

The engineer will start with a diagnostic check - testing the boiler's output, checking system pressure, looking for fault codes, and assessing the diverter valve or motorised valves depending on your system type. This diagnostic phase commonly takes 20 to 40 minutes. Most engineers carry stock of common spare parts for popular boiler brands, so if it turns out to be a diverter valve or thermistor on a Worcester Bosch, Vaillant, or Ideal boiler, there's a good chance the repair can be completed on the same visit.

Call-out charges in the Devon area typically range from 60 to 100 pounds, with hourly labour on top - commonly 60 to 90 pounds per hour. Parts are charged separately. A diverter valve replacement with labour commonly comes to between 150 and 350 pounds in total. A thermistor or sensor replacement usually falls at the lower end - around 100 to 200 pounds including parts. A motorised valve replacement typically costs between 100 and 200 pounds depending on access and the valve type.

Always ask the engineer for a written quote before work begins. Make sure they can show you their Gas Safe registration card - you have every right to ask for this, and a reputable engineer will expect you to. You can also verify any Gas Safe engineer's credentials directly on the Gas Safe Register website.

Common Questions from Barnstaple Homeowners

Why does my heating work but I have no hot water?

The most common reason on a combi boiler is a faulty diverter valve, which gets stuck directing heat to the radiators instead of switching to the hot water circuit. On systems with a cylinder, a failed motorised valve or cylinder thermostat is more likely. Low boiler pressure and programmer faults are also worth ruling out first as they're easy to check yourself without any tools or specialist knowledge.

Can I fix a diverter valve myself?

No. Replacing a diverter valve involves working inside the boiler on components connected to the gas supply. This work must legally be carried out by a Gas Safe registered engineer in the UK - it's not just a recommendation, it's a legal requirement. Attempting the repair yourself is unsafe and could invalidate your boiler warranty. The job itself is a common one and most engineers can complete it in under two hours on a standard visit.

How much does it cost to fix no hot water on a combi boiler in Barnstaple?

Most common repairs for this problem fall somewhere between 100 and 350 pounds including parts and labour, depending on what's failed. A thermistor replacement is typically at the lower end of that range, while a diverter valve replacement on a more complex boiler model can reach the higher end. Factor in the call-out charge on top - this is commonly between 60 and 100 pounds in the Barnstaple and wider Devon area. Always get a written quote before the work starts.

How long does a boiler repair take in Barnstaple?

For the most common faults - a diverter valve or motorised valve replacement - most repairs take between one and two hours once the engineer is on site. If a part needs to be ordered, which can happen with older or less common boiler models, you may need a follow-up visit. Engineers who carry a good stock of spare parts for popular brands like Worcester Bosch, Vaillant, and Ideal can often complete the job in a single call-out, getting your hot water restored the same day.