No Hot Water But Heating Works - What to Check in Barrow-in-Furness

Published October 2026 | No hot water but heating works what to check

We asked our Boiler Repair engineers the questions Barrow-in-Furness homeowners ask most. If your radiators are warm but your taps are running stone cold, this guide walks you through what is likely going wrong, what you can safely check yourself, and when you need a professional.

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

When your heating works but your hot water doesn't, it tells you something important straight away: the boiler is firing. It's producing heat. The problem is in how that heat is being distributed or directed, not in the combustion process itself. That's actually useful information, because it narrows the fault down considerably.

On a combi boiler - the most common type in modern UK homes - the same heat is used for both your central heating circuit and your domestic hot water. These two functions are controlled separately by different components, so one can fail while the other keeps working. On older systems with a hot water cylinder, there are additional parts in the chain that can fail independently of the boiler itself.

As Plumbing Correct's guide on this fault explains, there are typically nine likely causes depending on your boiler type, so identifying which system you have is the first step toward a fix. The most common culprits are a faulty diverter valve, a blocked plate heat exchanger, a failed zone valve, or a thermostat issue - all of which are repairable without replacing the whole boiler in most cases.

What should I check before calling an engineer?

There are a few safe checks any homeowner can carry out before picking up the phone. None of them involve touching gas components or opening the boiler casing.

First, check the boiler pressure gauge. Most combi boilers need to sit between 1 and 1.5 bar when the system is cold. If it's below 1 bar, low pressure can prevent the hot water circuit from working properly. You can top it up using the filling loop - typically a flexible silver hose underneath the boiler - following the instructions in your manual.

Second, check your programmer or thermostat settings. Hot water and heating are often on separate schedules, and it's surprisingly common for a programme to have been accidentally switched off. If you have a smart thermostat like a Hive or Nest, open the app and look specifically for a hot water schedule - it's separate from the heating one.

Third, try resetting the boiler. Most modern boilers have a reset button on the front panel. A temporary fault or lockout can sometimes be cleared with a simple reset. If the boiler locks out again within an hour, that's a sign something needs looking at properly.

Finally, run the hot tap for a couple of minutes. If water starts warm and cools rapidly, that points to a different fault than water that never warms up at all. These details help an engineer diagnose the problem faster when you do call.

Could a faulty diverter valve be the cause?

On a combi boiler, the diverter valve is the first thing our engineers suspect when heating works but hot water doesn't. The diverter valve is the component that switches the boiler's output between heating your radiators and heating your domestic water. When it's working, it responds to demand - if you turn on the hot tap, it diverts heat to the plate heat exchanger; when you're just running the heating, it keeps heat in the central heating circuit.

When this valve starts to fail, it commonly sticks in the central heating position. The boiler fires, the radiators heat up, but no heat reaches your hot water at all. A telling sign is that turning the heating off sometimes makes the hot water start working again - that's classic stuck diverter valve behaviour.

As BOYLA's engineers note on combi boiler faults, the diverter valve is one of the most frequently diagnosed causes of this exact symptom pattern, and it's usually fixable without needing a full boiler replacement. Replacing a diverter valve typically costs between 150 and 350 pounds including parts and labour, depending on the boiler make and model. Worcester Bosch, Baxi, and Ideal all use different valve designs, so parts pricing varies. This is a job that must be done by a Gas Safe registered engineer - working on internal gas appliance components is a legal requirement under the Gas Safety (Installation and Use) Regulations 1998.

What if I have a hot water cylinder rather than a combi boiler?

Many properties in Barrow-in-Furness - particularly older terraces and semi-detached houses - still use a conventional or system boiler paired with a hot water cylinder. The diagnostic process is different for these systems because there are more components in the chain between the boiler and your hot tap.

Here's where to look on cylinder-based systems:

Motorised zone valve

This valve controls whether hot water flows from the boiler to the cylinder. If it fails or seizes, the boiler will happily heat the radiators but send nothing to the cylinder. Replacing a zone valve typically costs between 100 and 200 pounds.

Cylinder thermostat

This sits on the outside of the cylinder and tells the system when the water is hot enough. If it's failed or set incorrectly, the cylinder never calls for heat. It should be set between 60 and 65 degrees Celsius - the right range to heat water properly and prevent Legionella growth.

Immersion heater

Many cylinders have an electric immersion heater as a backup. If the boiler-fed side has failed, switching this on gives you hot water while you wait for a repair. It's not cheap to run long-term at around 3kW, but it's a practical short-term solution.

On older systems in Cumbria, damp can affect wiring connections between the programmer, cylinder thermostat, and zone valve. Corroded connections are a common fault that's easy to miss without properly testing the circuit.

Could the thermostat or programmer settings be to blame?

Yes - and this catches people out more often than you'd expect. Modern heating systems, especially those with smart controls, separate hot water and heating into different zones or schedules. If the hot water programme has been accidentally switched off, or if a firmware update has reset the schedule, you'll get exactly this symptom: warm radiators, cold taps.

If you have a smart thermostat, check the app carefully. The hot water schedule is separate from the heating schedule and isn't always obvious. Make sure it's actually enabled and set to come on when you need it.

On older programmers with physical dials or switches, check that the hot water selector is set to "auto" or "on" rather than "off". We've attended jobs in Barrow-in-Furness where this was the only issue - a programme that had been nudged or reset during a power cut. It's always worth ruling this out before assuming the worst.

If the programmer itself is faulty rather than just mis-set, replacement typically costs between 80 and 200 pounds fitted. It's worth considering an upgrade to a smart thermostat at the same time, since separate hot water control is much clearer on modern systems and tends to reduce wasted energy.

What is a plate heat exchanger and could it be blocked?

On a combi boiler, the plate heat exchanger is the component that transfers heat from the boiler's primary circuit to your incoming cold water supply, producing your hot water on demand. It works through a series of thin metal plates - hot primary water passes one side, cold mains water passes the other, and heat transfers between them without the two water supplies mixing.

Over time, limescale can build up inside the plate heat exchanger, reducing the efficiency of heat transfer. You might notice lukewarm water rather than a complete absence of hot water, or the boiler may shut down on its high-temperature safety limits because heat has nowhere to go. Barrow-in-Furness generally benefits from moderately soft water, but scale can still accumulate in older systems over many years.

Descaling or replacing a plate heat exchanger typically costs between 200 and 500 pounds. On older boilers, it can make more sense to replace the unit entirely rather than spend that on a single component - particularly if other parts are also showing wear. Our engineers can run a quick assessment using Voltrade's GoFIX diagnostic tool to evaluate the overall condition of the boiler, so you're making that decision based on the full picture rather than just the immediate fault.

How much should I expect to pay for this type of repair?

Costs vary depending on what's failed, but here's a realistic guide based on typical UK repair prices:

• Diverter valve replacement: 150 to 350 pounds
• Plate heat exchanger replacement: 200 to 500 pounds
• Motorised zone valve (cylinder systems): 100 to 200 pounds
• Cylinder thermostat replacement: 80 to 150 pounds
• Programmer or smart thermostat replacement: 80 to 250 pounds
• Annual boiler service (which can catch developing faults): 80 to 120 pounds

Call-out charges in Cumbria typically range from 50 to 100 pounds, and many engineers will fold this into the total repair cost if you proceed with the work. As BOYLA's breakdown of hot water repair costs confirms, these component-level repairs are generally modest compared to full boiler replacement, and in most cases a targeted repair is the right financial decision.

If your boiler is over 12 to 15 years old and facing an expensive repair, get a replacement quote at the same time. A new combi boiler in Barrow-in-Furness typically costs between 1,500 and 3,000 pounds installed, depending on the model and any pipework changes needed. That context makes it easier to judge whether repair or replacement makes more sense.

When do I legally need a Gas Safe registered engineer?

Any time a repair involves working on internal gas appliance components, UK law requires the work to be carried out by a Gas Safe registered engineer. This covers replacing the diverter valve, plate heat exchanger, gas valve, or any other internal boiler part. It's a legal requirement under the Gas Safety (Installation and Use) Regulations 1998 - not just industry best practice.

You can verify any engineer's Gas Safe registration at the official Gas Safe Register. A properly registered engineer should carry their ID card and will show it on request. Don't be shy about asking.

The homeowner checks covered earlier in this article - topping up pressure, checking programmer settings, resetting the boiler, running taps - are all safe without any qualifications. Anything that involves opening the boiler casing or touching gas connections needs a professional. All engineers booked through Voltrade are Gas Safe registered, which is a simple way to make sure you're getting compliant, qualified work.

Could low boiler pressure be causing the problem?

Yes - low pressure is one of the simpler causes of hot water failure and one of the first things our engineers check on a call-out. Most combi boilers have a pressure gauge on the front showing a reading in bar. Correct operating pressure is typically between 1 and 1.5 bar when the system is cold.

If pressure drops below about 0.8 to 1 bar, many boilers will continue heating the central heating circuit but struggle to produce adequate hot water flow. Some will lock out entirely. Topping up the pressure yourself using the filling loop is safe and doesn't require a Gas Safe engineer - your boiler manual will have model-specific instructions, but the general process is simple: turn the boiler off, slowly open the filling loop valves until the gauge reads around 1.2 bar, then close the valves and restart the boiler.

If the pressure keeps dropping back down within days, you have a leak somewhere in the system. That needs an engineer to find and fix - small leaks on radiator valves or pipework joints are a common cause and are usually inexpensive to repair.

How can I prevent this happening again?

Annual boiler servicing is the most reliable way to catch developing faults before they become a cold shower on a January morning in Barrow-in-Furness. A service - typically 80 to 120 pounds - gives a Gas Safe engineer the chance to inspect the diverter valve, heat exchanger, pressure, flue, and all major components. Many faults give warning signs before they fail completely, and an experienced eye catches them early.

A few other habits that help keep things running well through Cumbria winters:

• Check boiler pressure monthly and top it up as needed.
• If you have a hot water cylinder, keep the thermostat set between 60 and 65 degrees.
• Bleed radiators once a year to remove trapped air - airlocks can indirectly affect hot water performance on conventional systems.
• Book your annual service in September or October, before the system is under heavy winter load.

If your boiler is approaching 10 years old, a boiler cover plan is worth considering. Call-out and repair costs are predictable, and you're less likely to be without hot water for extended periods waiting for an available engineer during peak winter demand.

To sum up: when your heating works but your hot water doesn't, you're almost certainly dealing with a component fault rather than a fundamental boiler failure. The most likely causes on a combi boiler are a stuck diverter valve or a scaled-up plate heat exchanger. On cylinder systems, look at the zone valve, cylinder thermostat, or programmer settings. Run the basic checks yourself first, then get a Gas Safe registered engineer in to diagnose and fix whatever's failed - in most cases it's a single visit and a repair cost well below what a replacement would set you back.

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

The most common cause is a faulty diverter valve that has stuck in the central heating position. Other likely causes include a blocked plate heat exchanger, low boiler pressure, or a programmer that has the hot water schedule switched off. A Gas Safe engineer can diagnose the specific fault quickly, and most are fixable in a single visit.

How long does it take to fix no hot water on a boiler?

In most cases a Gas Safe engineer can diagnose and repair the fault in a single visit lasting two to four hours. If a specific part needs ordering - which is more likely with older or less common boiler models - a return visit may be needed, typically within a few days depending on parts availability in your area.

Is it safe to keep using my heating while I have no hot water?

Generally yes. If the boiler is firing and the radiators are working, the central heating side of the system is functioning normally. You can continue using the heating while you wait for a repair. If the boiler is making unusual noises, showing error codes, or the pressure is erratic, turn it off and call an engineer sooner rather than later.

How do I know whether to repair or replace my boiler?

A common rule of thumb is that if the repair cost exceeds roughly a third of the cost of a new boiler and the unit is already over 12 years old, replacement often makes better long-term sense. A Gas Safe engineer can give you an honest assessment once they have diagnosed the fault, and comparing both options on cost and likely remaining lifespan is the right way to decide.