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

Published September 2026 | Boiler Repair

In the First 10 Minutes

When your radiators are warm but your hot taps run cold, that specific combination of symptoms usually points to a small number of faults rather than a complete boiler failure. Your boiler is clearly producing heat - the question is why that heat isn't reaching your hot water. Start here before you do anything else.

1. Check your programmer or timer. This is the most common cause our engineers find in Arundel homes. Many combi boilers and system boilers have completely separate time schedules for heating and hot water. It's easy to accidentally switch off the hot water programme while adjusting your heating settings. Check that hot water is set to "on" or scheduled for the current time.
2. Check your hot water temperature setting. On most boilers there's a separate dial or digital setting for domestic hot water (DHW). On Worcester Bosch models it's typically labelled with a tap symbol. Make sure it hasn't been turned down to its lowest setting accidentally.
3. Check your boiler pressure. Look at the pressure gauge on the front of your boiler. It should sit between 1 and 1.5 bar when the system is cold. If it's dropped below 0.8 bar, the boiler may be limiting functionality to protect itself. You can top up the pressure using the filling loop - your boiler manual shows how, and it takes about two minutes.
4. Note any fault codes. Modern boilers from Vaillant, Baxi, Ideal, and Viessmann display error codes when something's wrong. Write down any code showing on the display. The code plus your boiler model will often tell you precisely what's failed before an engineer even arrives.

Don't keep resetting the boiler if it's locked out. One reset attempt is fine. Repeatedly cycling it can mask the fault and makes the engineer's diagnosis harder and slower.

Within the First Hour

If those basic checks haven't fixed the problem, you're most likely dealing with one of three faults: a stuck diverter valve, a faulty motorised zone valve, or a failed hot water thermostat. The next step is narrowing it down by identifying your boiler type.

Combi boiler - no separate hot water cylinder anywhere in the house. These are common in Arundel properties, particularly in newer builds and converted flats. In a combi, a diverter valve physically switches the heat exchanger output between your radiators and your hot taps. When it sticks in the heating position, your radiators warm up perfectly while your hot taps stay cold. This is the single most common cause of this fault in combi systems.

System or heat-only boiler with a cylinder - you'll have a hot water tank, usually in an airing cupboard. In this case, the most likely culprits are the motorised zone valve (which controls flow to the cylinder), the cylinder thermostat, or the hot water programme not calling for heat at the right time. Go to your airing cupboard and feel the cylinder. It should feel warm about two-thirds of the way up if it's been heated recently. If it's cold throughout, heat isn't reaching it at all - pointing to the zone valve or wiring. If it's warm but your taps run cold, you may have an airlock in the pipework.

You can run the Voltrade GoFIX diagnostic tool if you're not sure which fault type applies to your setup. It walks you through the questions systematically and helps you describe the problem accurately to an engineer - which can cut diagnosis time on the day.

Same Day

Most of the underlying causes of this fault aren't DIY repairs. The diverter valve sits inside the boiler, and touching gas components without Gas Safe registration is illegal - not just a technicality, but a genuine safety risk to you and your household. What you can do today is get organised for an engineer's visit and make the job as quick as possible.

Calls to make:

1. Contact a Gas Safe registered boiler engineer. In West Sussex, availability varies by season - in colder months waiting times can stretch, but a hot-water-only fault with heating still working isn't usually classed as an emergency unless you have young children or elderly residents at home.
2. If you're renting, call your landlord straight away. They have a legal obligation to provide hot water and must arrange repair promptly.

Information to have ready when you call:

• Boiler make, model, and age - usually on a sticker on the boiler front or inside the casing
• Any fault code on the display
• When the problem started, and whether anything changed around that time - a power cut, a pressure drop, someone adjusting settings
• Whether you ever get a brief burst of hot water that then cuts out - this points to a different fault to total failure

While you wait, if you have an immersion heater on your hot water cylinder, switch it on. There's typically a switch in the airing cupboard, sometimes inside the cupboard near the tank. An hour on the immersion heater is usually enough to heat a standard cylinder for bathing. It costs more than gas, but that's what it's there for.

The Repair Visit

Our engineers covering the Arundel area and across West Sussex carry common replacement parts on the van - diverter valves and zone valves for popular boiler makes are standard stock. Less common components for older or more unusual models may need to be ordered, which can mean a return visit.

Here's what a typical visit looks like:

1. Diagnosis - 15 to 30 minutes. The engineer confirms the fault, tests the boiler operation, and checks the diverter valve or zone valves depending on your setup.
2. Component replacement - for a diverter valve on a combi, this typically takes 45 minutes to an hour and a half. Zone valve replacement on a system boiler is similar. More complex faults like a plate heat exchanger replacement take longer.
3. System testing - the engineer runs the boiler through full heating and hot water cycles before leaving, and checks for any pressure changes or leaks.

Typical costs in the UK for 2026:

• Diverter valve replacement (combi boiler): typically between 150 and 350 pounds including parts and labour
• Motorised zone valve replacement: typically between 120 and 280 pounds
• Cylinder thermostat replacement: typically between 80 and 150 pounds
• Plate heat exchanger: typically between 300 and 700 pounds - this is a more significant repair and is worth weighing against boiler age

If your boiler is over 10 to 12 years old and the repair cost is approaching 500 pounds or more, ask the engineer for an honest assessment of the boiler's overall condition. Older Baxi or Ideal boilers reaching this point sometimes make more economic sense to replace than to keep repairing.

The Following Week

After the repair is done, spend a few days checking that hot water performs consistently before you consider the job closed.

• Run your hot taps at different times of day and confirm the temperature is steady - ideally 55 to 60 degrees Celsius at the tap.
• Check your boiler pressure every couple of days. A pressure drop after a repair can indicate a small leak that wasn't obvious during the visit.
• If your boiler was making unusual sounds before the fault - clunking, banging, or a kettle-like noise - note whether those have cleared. A diverter valve fault can occur alongside limescale buildup, which is common in areas with hard water. Parts of this area do have moderately hard water, which accelerates wear on heat exchangers over time.
• Test both heating and hot water circuits separately. Occasionally a repair to one circuit reveals a marginal problem in the other that wasn't apparent before.

If anything doesn't seem right in the first week, call the engineer back. Any engineer worth using will want to know about issues with their recent work and will return to investigate.

Long Term

The most reliable way to avoid finding yourself without hot water on a cold Arundel morning is routine annual servicing. This is the single most effective prevention available, and it's not expensive relative to repair costs.

A Gas Safe registered engineer will inspect the diverter valve condition, test zone valves, check the heat exchanger, verify combustion efficiency, and flag components that are showing wear before they fail. Annual servicing typically costs between 80 and 130 pounds - a fraction of even the cheapest emergency call-out and repair.

Beyond servicing, a few investments make a real difference over time:

• Inhibitor treatment - if your central heating system has never been treated with corrosion inhibitor, ask your engineer to add some at the next service. Sludge and iron oxide in the system can block valves and significantly shorten boiler lifespan.
• Magnetic filter - fitting one to the return pipe captures iron particles before they circulate. Many Arundel homeowners who've had repeated boiler faults find this resolves the pattern of recurring problems.
• Cylinder thermostat check - if you have a hot water cylinder, confirm the thermostat is set to 60 degrees Celsius. This prevents legionella growth without overheating the water or wasting energy.
• Plan for replacement on older boilers - if your boiler is over 15 years old, start budgeting. A new A-rated condensing boiler typically costs between 1,800 and 3,500 pounds installed, reduces heating bills, and removes the risk of repeated repair bills on an ageing system.

Timeline Questions

How long does a no-hot-water boiler repair typically take to complete?

Most diverter valve or zone valve replacements take between one and three hours from the engineer arriving to the system being fully tested. More involved repairs like a plate heat exchanger can take longer and may require a return visit if parts aren't on the van. For the majority of call-outs in Arundel, you're looking at roughly two hours on site.

Can I still shower or use the taps while waiting for an engineer?

Your cold water supply is completely unaffected by a boiler fault, and your heating will usually continue working normally. If you have an immersion heater on your cylinder, switch it on about an hour before you need hot water. If you have a combi boiler with no cylinder, you'll need to wait until the fault is repaired - there's no backup heat source for domestic hot water in that setup.

How quickly can a Gas Safe engineer reach me in the Arundel area?

For a non-emergency hot water fault where heating is still working, most Gas Safe registered engineers can reach Arundel within one to two working days. Same-day visits are possible through Voltrade, though availability tightens in winter when demand peaks across West Sussex. If you have no hot water and no heating - or if there are vulnerable people in the household - most engineers will prioritise your call.

Is this always a boiler fault, or could it be something simpler?

Not always a boiler fault. In a significant number of call-outs, the cause turns out to be a programmer setting, a tripped circuit, or a thermostat that's been accidentally adjusted. Our engineers find that many no-hot-water visits are resolved without any part replacement at all - a setting correction or a single reset is enough. That's exactly why the basic checks in the first 10 minutes are worth doing carefully before you call anyone.