No Hot Water but Heating Works in Ashington - What to Check First

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

Most people assume that if their radiators are pumping out heat, the boiler must be working perfectly and the hot water fault lies somewhere else entirely. That assumption sends homeowners on a wild goose chase - checking header tanks, fiddling with taps, blaming the programmer - while the real culprit sits inside the boiler the whole time. The truth is, heating and hot water share the same boiler but they don't always share the same fault.

Myth: If the Heating Works, the Boiler Is Fine

The reality

This is probably the most persistent myth our engineers come across. A boiler can fire up perfectly, heat your radiators to a comfortable temperature, and still fail to deliver a single drop of hot water to your taps. The reason comes down to how modern boilers are designed on the inside.

In a combi boiler - which is the most common type in homes across Ashington and the wider Northumberland area - the same unit handles both central heating and domestic hot water. But it does this through separate internal circuits. When you open a hot tap, the boiler is supposed to divert its energy away from the heating circuit and towards heating your water directly. The component that manages this is called the diverter valve. When it gets stuck or wears out, the boiler happily keeps heating your radiators while your taps run cold.

The diverter valve is one of the most commonly replaced components our engineers find during boiler repair call-outs, particularly in older Worcester Bosch, Vaillant, and Baxi models that have been running for more than seven or eight years. Boyla's guide to boiler faults by type confirms that a stuck or failing diverter valve is a leading cause of this exact symptom - heating on, hot water off.

Myth: No Hot Water Always Means You Need a New Boiler

The reality

The jump from "no hot water" to "I need a full boiler replacement" is an expensive leap that isn't usually necessary. The vast majority of cases where heating works but hot water doesn't come down to a single faulty component, not a failed boiler.

Here is what our engineers typically find when they diagnose this fault:

1. A stuck diverter valve - commonly found in combi boilers and typically costs between 150 and 300 pounds to replace, including parts and labour.
2. A faulty plate heat exchanger - this component transfers heat to your domestic hot water in combi boilers. When it scales up with limescale or develops an internal crack, hot water suffers while heating continues. Replacement typically costs between 200 and 400 pounds.
3. A failed cylinder thermostat or motorised zone valve - relevant for system boilers and heat-only (regular) boilers with a hot water cylinder. These parts are considerably cheaper to replace, commonly falling in the 80 to 200 pound range.
4. A faulty hot water sensor - the boiler's NTC thermistor (temperature sensor) may be misreading the water temperature, causing the boiler to think the water is already hot enough when it isn't.

None of these repairs require a new boiler. Guidance on this specific fault pattern makes it clear that targeted component repairs resolve the issue in most cases. Our Voltrade GoFIX diagnostic tool can help identify the likely fault before an engineer even arrives, narrowing down the component that needs attention so the repair visit is efficient.

Myth: Resetting the Boiler Will Sort It Out

The reality

Resetting your boiler is always worth trying - it takes about 30 seconds and costs nothing. But it isn't a fix, and it's definitely not a substitute for a proper repair.

If the boiler has a fault code showing on its display, a reset might clear the code temporarily. But if the underlying component is failing, the fault will return. Sometimes within minutes. When our engineers attend no-hot-water call-outs in Ashington, they often find boilers that have been reset repeatedly over days or even weeks. Each reset buys a short window of hot water, but the diverter valve or sensor that's degrading keeps failing. The homeowner ends up running through the reset cycle several times a day - which is frustrating and, over time, can put unnecessary strain on other components.

A reset can legitimately fix a boiler that's gone into lockout because of a temporary pressure drop, a brief airlock, or a one-off ignition failure. These are isolated events. If the fault keeps returning after every reset, you're dealing with a component that needs replacing, not a boiler that just needs waking up.

Before calling an engineer, check your boiler's pressure gauge. It should sit between 1 and 1.5 bar when the system is cold. If it's below 0.5 bar, the boiler may be struggling to heat water properly. Repressurising the system using the filling loop is something most homeowners can manage themselves - your boiler manual will walk you through it. But if the pressure keeps dropping, that points to a leak or a failing pressure relief valve, and a Gas Safe registered engineer needs to investigate.

Myth: The Programmer or Thermostat Must Have Changed Settings

The reality

When heating works but hot water doesn't, homeowners frequently suspect the programmer or smart thermostat. It makes intuitive sense - if one function is on and the other isn't, surely the controls have been set up wrong?

In practice, programmer faults are rarely the cause. Most modern thermostats and programmers - whether it's a Nest, Hive, or a standard Drayton or Honeywell unit - have separate channels for heating and hot water. It is possible to accidentally set hot water to "off" or "once" instead of "twice" or "continuous", particularly after a power cut which can reset some programmers to factory defaults. Check these settings first - it's a two-minute job and occasionally solves the problem entirely.

But if the settings look correct and hot water still isn't coming through, the controls aren't to blame. The fault is almost certainly inside the boiler or, for homes with a separate cylinder, in the cylinder controls. Our engineers use the Voltrade GoFIX diagnostic process to rule out controls issues quickly and focus attention where it actually needs to be.

Myth: Fixing a Diverter Valve Is a DIY Job

The reality

The diverter valve sits inside the boiler casing. Getting to it involves isolating the gas supply, draining down part of the system, and working in close proximity to gas connections and live electrical components. The risk of creating a gas leak or introducing air into the sealed system is real. UK guidance on boiler troubleshooting is consistent on this point: safe homeowner checks are limited to external ones, and everything inside the casing belongs to a qualified professional.

What you can safely do yourself, without any qualifications:

• Check and adjust programmer or thermostat settings
• Check the boiler pressure gauge and repressurise using the filling loop if needed
• Note any fault or error codes displayed on the boiler panel
• Run the Voltrade GoFIX check to help confirm the likely cause before calling an engineer
• Check whether the hot water cylinder feels warm near the top (for system and regular boilers)
• Switch on the immersion heater as a temporary measure if your cylinder has one

Everything else - the diverter valve, plate heat exchanger, thermistor, zone valves - needs a Gas Safe engineer. In Northumberland, our engineers carry the most commonly needed replacement parts for popular models including Worcester Bosch, Ideal, Potterton, and Vaillant, so repairs can often be completed in a single visit.

What Actually Matters - Expert Advice

When you've got heating but no hot water, the first thing to do is identify your boiler type. This changes everything about the likely cause and the fix required.

Combi boiler (no cylinder, no tank in the loft): The diverter valve and plate heat exchanger are the prime suspects. The boiler handles everything internally, so the fault is almost certainly inside the unit. Check the pressure, note any fault codes showing on the display, and call a Gas Safe registered engineer. Don't wait weeks - a failing diverter valve can deteriorate further and bring down the heating circuit with it.

System boiler with a cylinder: The boiler heats your radiators and a separate cylinder stores your hot water. If heating works but the cylinder isn't getting hot, the issue is commonly the motorised valve (sometimes called a mid-position or three-port valve), the cylinder thermostat, or - more rarely - the boiler itself failing to trigger the hot water zone. Hold your hand near the top third of the cylinder. If it feels completely cold after the boiler has been running, the zone valve or thermostat has most likely failed.

Regular (heat-only) boiler with a cylinder: Check the cylinder thermostat - a small cylindrical device strapped to the side of the hot water tank. It should typically be set to around 60 degrees Celsius. If it's set correctly but the cylinder stays cold, either the thermostat has failed or the motorised valve serving the cylinder has seized. If your cylinder has an immersion heater, switch it on as a temporary measure while you arrange the repair.

In older properties across Northumberland, where regular boilers with separate cylinders are more common, our engineers frequently find that motorised valves have seized from lack of use during the summer months. These valves do have a manual override lever which can sometimes restore hot water temporarily, but operating it is a job for a qualified engineer - not a DIY fix.

One practical tip that saves time: if you have a Worcester Bosch, Ideal, or Baxi boiler, write down the error code showing on the display before you call. Engineers can often narrow down the fault from the code alone, which means they arrive with the right part and complete the repair in one visit rather than two.

Myth-Busting Questions

Will bleeding my radiators help restore hot water?

Bleeding radiators removes trapped air from the heating circuit and improves radiator performance, but it won't fix a hot water fault. The heating circuit and hot water circuit are separate - releasing air from one doesn't affect the other. If your radiators have cold spots at the top, bleeding them is sensible maintenance, but it won't bring your hot water back. After bleeding, check your boiler pressure and repressurise if it has dropped below 1 bar.

Could limescale be blocking my hot water pipes?

Limescale can block the plate heat exchanger inside a combi boiler over time, reducing flow and making hot water performance sluggish before it fails entirely. However, limescale blocking the pipes themselves is much less common, particularly in the Northumberland region where water tends to be soft to moderately soft. If your hot water has been getting weaker and cooler over months before stopping, a scaled plate heat exchanger is worth investigating. A completely scaled exchanger typically needs replacing rather than descaling.

Is it safe to keep using the heating while I wait for a repair?

In most cases, yes. If the boiler is running normally, producing no unusual sounds and showing no error codes, continuing to use the heating while you arrange a repair for the hot water is fine. The boiler is operating within its normal parameters for the heating function. However, if the boiler is displaying a fault code, making banging or kettling noises, or if you can smell gas at any point, turn the boiler off immediately and call the Gas Emergency Service on 0800 111 999. Do not use the boiler again until a Gas Safe registered engineer has checked it.

Frequently Asked Questions

How much does it typically cost to fix no hot water on a boiler in Ashington?

Repair costs depend on the fault found. A diverter valve replacement in a combi boiler typically costs between 150 and 300 pounds including parts and labour. A plate heat exchanger replacement commonly falls between 200 and 400 pounds. For system and regular boilers, a cylinder thermostat or motorised valve repair usually costs between 80 and 200 pounds. Diagnostic call-out fees in the area typically run between 60 and 100 pounds, and many engineers include this in the total repair cost if you proceed with the work.

How long does a boiler repair for no hot water usually take?

Most diverter valve and sensor replacements can be completed within one to two hours once the engineer arrives with the correct part. Plate heat exchanger replacements on combi boilers typically take two to three hours. If a part needs ordering rather than being carried on the van, there's usually a wait of one to two working days. Using a diagnostic tool like Voltrade GoFIX before the engineer visits means the likely fault is already identified, so the right parts can often be brought on the first call.

Does a Gas Safe engineer need to provide paperwork after a boiler repair?