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

Published September 2026 | Boiler Repair

How long should your boiler last and what affects that

Your boiler's lifespan depends heavily on how well it is maintained and, in a place like Aldershot, how hard the local water supply is. Hampshire's water sits in the moderately hard category, which means limescale gradually builds inside the heat exchanger and pipes over the years. Left unchecked, that scale shortens component life considerably and is one of the most common reasons hot water fails before the heating does.

A well-maintained combi boiler from a reputable manufacturer - Worcester Bosch, Vaillant, Baxi, or Ideal - should last around 12 to 15 years before you are looking at replacement. Cheaper models or boilers that have never had an annual service typically fail well before the 10-year mark. The specific fault covered in this article - hot water not working while heating runs fine - is overwhelmingly caused by a handful of internal components rather than the boiler itself dying. Understanding why that happens gives you a better chance of extending your boiler's life rather than replacing it prematurely.

Several factors directly affect how long your system lasts:

1. Water hardness - harder water deposits limescale faster, clogging heat exchangers and reducing efficiency
2. Annual servicing - a boiler that gets yearly attention will flag small problems before they become expensive ones
3. System pressure - repeatedly running at incorrect pressure stresses internal seals and valves
4. Quality of the original installation - poor installation causes premature wear on multiple components simultaneously
5. Usage patterns - a household with high hot water demand stresses the diverter valve far more than an average-use home

The good news is that most of these factors are within your control. A boiler that reaches 15 years in good working order is almost always one that has had consistent professional attention and sensible day-to-day management from the household.

The maintenance that actually makes a difference

When our engineers visit homes across Aldershot for boiler repairs, there is a clear pattern. The boilers that have had consistent annual servicing rarely need major component replacements before 12 years. The ones left alone for four or five years are where we see diverter valves seized solid, heat exchangers completely furred up, and thermistors sending wildly inaccurate readings.

The maintenance tasks that extend boiler life fall into two categories - what your engineer does annually and what you can manage yourself between visits.

Inhibitor treatment is one of the most overlooked. Central heating inhibitor is a chemical added to the system water that prevents internal corrosion and reduces sludge build-up. It should be topped up or refreshed every few years, and its concentration tested at every service. A system running without inhibitor develops black sludge that clogs the diverter valve and damages the pump far faster than normal wear would.

Power flushing is worth considering if your system is older and has never had one. It forces a cleaning solution through the pipework at high pressure, removing years of accumulated sludge. For a typical three-bedroom home in Hampshire, expect to pay somewhere between 400 and 700 pounds for a full power flush. That sounds significant, but it commonly extends boiler life by several years and restores heating efficiency that has been quietly degrading.

Descaling the heat exchanger periodically is essential in hard water areas. When a homeowner calls us reporting no hot water but radiators working fine, a limescale-clogged plate heat exchanger is one of the first things we check using the Voltrade GoFIX diagnostic tool, which quickly identifies whether flow restriction is the underlying cause before any components are removed.

Warning signs your boiler is reaching end of life

Not every boiler fault means replacement, but some patterns do indicate a boiler is declining rather than just needing a targeted repair.

Increasingly frequent breakdowns are the clearest signal. If you are calling out an engineer more than once a year for different faults, the boiler is telling you something. A single diverter valve replacement is normal wear. Replacing the diverter valve, then the pump, then a printed circuit board within three years suggests a boiler that is degrading throughout rather than experiencing isolated failures.

Sharply falling efficiency is another indicator. Older boilers that previously heated the house comfortably but now struggle, or gas bills that have risen significantly without any change in usage habits, point to a boiler working harder than it should to deliver the same output. This kind of hidden inefficiency often precedes a component failure by six to twelve months.

Unusual noises combined with the hot water fault - banging, kettling, or persistent clicking when the boiler fires - suggest limescale damage extensive enough that cleaning may not resolve it fully. Kettling in particular points to severely restricted water flow through the heat exchanger.

Parts availability matters too. For boilers over 12 years old, manufacturers sometimes discontinue spare parts. A Worcester Bosch or Vaillant-trained technician will tell you quickly whether the repair is viable or whether the part you need is becoming difficult to source.

If your boiler is under eight years old and in reasonable condition, a hot water fault is almost certainly worth repairing. At ten years or older, the repair-versus-replace calculation becomes more nuanced and needs an honest look at the numbers.

Repair vs replace - the honest calculation

When hot water stops working but the heating is fine, the most common culprit in a combi boiler is the diverter valve. This component redirects water flow between the central heating circuit and the hot water circuit on demand. When it fails, it typically sticks in the heating position - hence radiators working perfectly while the taps run cold. It is a very specific, diagnosable fault.

A diverter valve replacement typically costs between 150 and 300 pounds including parts and labour, depending on the boiler make and how accessible the component is. That is a sensible repair on a boiler under 10 years old. Other common causes carry similar repair costs:

• Thermistor replacement - typically 80 to 150 pounds. The thermistor monitors water temperature; a faulty one causes the boiler to shut down hot water production as a safety measure, even when the heating circuit is unaffected.
• Plate heat exchanger descale or replacement - a professional descale typically costs 100 to 200 pounds; full replacement of the heat exchanger runs from 250 to 450 pounds depending on the model and manufacturer.
• Printed circuit board fault - these are expensive at 200 to 400 pounds for parts alone, which shifts the repair-versus-replace decision considerably on boilers over ten years old.

The rough rule of thumb used by experienced engineers is this: if the repair cost exceeds half the price of a comparable new boiler and your existing boiler is over 10 years old, replacement usually makes more financial sense over a three-year horizon. A new A-rated boiler will also cut gas consumption compared to a degraded older unit running at reduced efficiency.

One point that cannot be overstated: always insist on a Gas Safe registered engineer for any boiler work. Gas Safe registration is a legal requirement in the UK - not optional - and you should ask to see the engineer's ID card before any work begins. No legitimate engineer will object to showing it.

Annual service - what it should include

A proper boiler service is not just a visual inspection and a ticking of boxes. Our engineers carry out a specific set of checks that directly protect the components most likely to cause a no-hot-water fault down the line.

A thorough annual service should cover:

1. Flue gas analysis - checking combustion efficiency confirms the burner is running correctly and cleanly
2. Heat exchanger inspection - looking for limescale build-up or signs of corrosion that would restrict water flow
3. Diverter valve check - verifying it moves freely between heating and hot water modes and is not beginning to stick
4. Thermistor testing - confirming the sensor is providing accurate temperature readings to the control board
5. Gas pressure and flow rate - ensuring the boiler is receiving adequate gas supply at the correct pressure
6. System pressure check - topping up if needed and noting any signs of a slow pressure drop between visits
7. Inhibitor concentration test - testing the central heating water with a test strip to confirm adequate protection
8. Condensate trap clearance - removing any blockage that could cause shutdown during cold weather
9. Safety device testing - verifying the overheat thermostat and pressure relief valve function correctly
10. Visual check for leaks - inspecting all connections and the heat exchanger body for any seepage or staining

In Hampshire, where water hardness varies across the county, your engineer should specifically comment on limescale risk for your property and recommend whether a scale reducer or inhibitor refresh is advisable before the next service. Using the Voltrade GoFIX diagnostic tool at the start of the service allows our engineers to identify any underlying faults before the physical inspection, making the process faster and more targeted.

A boiler service typically costs between 80 and 120 pounds annually. That investment is considerably less than a 300-pound emergency call-out for a failed diverter valve - a fault that a thorough service commonly catches months before it becomes a full breakdown.

Simple habits that extend boiler life by years

Beyond the annual service, there are practical things any homeowner can do to keep a boiler running well for longer. None of these require technical knowledge - just a bit of attention.

Keep system pressure between 1 and 1.5 bar when the system is cold. If your pressure gauge regularly drops, you have a slow leak somewhere that needs finding. Repeatedly repressurising the system masks the problem while the underlying issue causes progressive corrosion to pipework and components.

Bleed radiators at the start of each heating season. Air locks make the pump work harder and reduce heat distribution efficiency. Cold spots at the top of radiators are your signal that bleeding is overdue. It takes about 10 minutes for a whole house and costs nothing.

Do not ignore warning lights or error codes. Modern boilers display fault codes for a reason. A code indicating a temperature sensor issue or low flow rate is often the first sign that a hot water problem is developing. Catching it early usually means a cheaper fix and avoids the loss of hot water entirely.

Run the hot water for a minute each week if the property has been unoccupied. This prevents the diverter valve from seizing in position during periods of inactivity - one of the most common causes of the heating-works-but-no-hot-water fault that our Aldershot engineers deal with after customers return from holidays. It is a simple habit that prevents an avoidable call-out.

Insulate your condensate pipe if it runs outside the property. A frozen condensate pipe causes the boiler to lock out completely and is entirely preventable with basic pipe lagging, which costs just a few pounds from any DIY retailer. It is one of the most cost-effective maintenance steps you can take before winter.

Check your programmer settings before calling an engineer. After a power cut or a clocks-change weekend, hot water programmes sometimes reset to default. Make sure the hot water is actually scheduled to come on at the times you expect before assuming there is a fault with the boiler itself.

Maintenance questions

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

In a combi boiler, this is nearly always a diverter valve fault. The diverter valve switches the boiler between heating mode and hot water mode when a tap is opened. When it sticks or fails, the boiler remains locked in heating mode - radiators get hot but taps stay cold. Other common causes include a faulty thermistor, a blocked plate heat exchanger, or a flow sensor fault. A Gas Safe registered engineer can diagnose which component is responsible, typically within a single visit using diagnostic tools. On system boilers with a separate cylinder, a failed motorised zone valve or a cylinder thermostat fault can produce the same symptom.

How much does a diverter valve replacement cost in the UK?

A diverter valve replacement in the UK typically costs between 150 and 300 pounds including parts and labour. The exact price depends on your boiler make - Worcester Bosch and Vaillant parts tend to sit at the higher end of that range compared to Baxi or Ideal. Some engineers charge a separate call-out fee on top of the repair cost; others include the diagnosis in the overall price. Always get a written quote before work begins and confirm the engineer holds current Gas Safe registration, which is a legal requirement for all gas appliance work in the UK.

Can limescale cause a boiler to stop producing hot water?

Yes, and it is a particularly common cause in hard water areas across Hampshire. Limescale builds up inside the plate heat exchanger - the component responsible for rapidly heating incoming cold mains water. When enough scale accumulates, flow is restricted to the point where the boiler's flow sensor cannot detect water movement and shuts down hot water production as a safety measure, even though the heating circuit continues to function. In moderate cases, a professional descale resolves the problem for a relatively modest cost. In severe cases the heat exchanger needs replacing entirely. Consistent annual servicing catches limescale accumulation before it reaches either of those stages.

How often should a boiler in an Aldershot home be serviced?

Once a year, without exception. Annual servicing is recommended by every major boiler manufacturer and is typically required as a condition of keeping the warranty valid on newer boilers. For homes in Aldershot and across Hampshire where water hardness can accelerate internal limescale build-up, consistent annual attention is particularly important. A service costs between 80 and 120 pounds and must be carried out by a Gas Safe registered engineer. The majority of boiler faults that result in emergency call-outs - including the no-hot-water fault this article covers - are detectable at a routine service before they develop into full breakdowns.