Hot Water Not Working?
Here's What You Need to Know
There’s nothing worse than waking up, turning on the tap, and realising your hot water is not working especially when your central heating seems to be working fine. It’s a frustrating and confusing situation that many homeowners face: heating but no hot water.
You might be wondering: why is my hot water not working when everything else seems fine? This guide will walk you through the most common causes, what to check yourself, and most importantly why it’s usually best to let a professional handle the fix.
Why Is My Hot Water Not Working?
When your central heating works but there’s no hot water, it usually means the boiler is firing up for one function (heating) but not the other (hot water). This could be due to a number of reasons some simple, some more technical.
Here are the most likely causes behind your hot water problems:
1. Faulty Diverter Valve (Combi Boilers)
If you have a combi boiler, a part called the diverter valve directs heat either to your radiators or to your hot water taps. When this valve fails or gets stuck on the heating side, you’ll get heating, but no hot water.
Signs of a diverter valve issue:
Radiators are working fine
Taps only run cold, even after waiting
Boiler fires up when heating is on, but not when a hot tap is opened
This is not a DIY job. A faulty diverter valve needs to be diagnosed and replaced by a Gas Safe registered heating engineer.
2. Broken Thermostat or Cylinder Thermostat
In some systems (like conventional boilers), hot water is stored in a cylinder. If the thermostat on that cylinder fails, your boiler won’t know when to heat the stored water even if your heating is running fine.
What to check:
Is the thermostat set to a high enough temperature (usually around 60°C)?
Is the thermostat clicking or responding when you turn it?
If you’re unsure or suspect it’s broken, it’s best to call a professional.
3. Timer or Programmer Settings
Sometimes the issue is as simple as incorrect settings. Your hot water might be scheduled to come on at a different time or not at all.
Check your boiler or wall-mounted programmer for:
Schedule settings for hot water vs heating
Manual override settings (try switching to “On” or “Advance” mode)
AM/PM confusion or power cuts that reset timers
4. Airlocks or Blocked Pipes
If air becomes trapped in the pipes, it can stop hot water from circulating properly, especially in gravity-fed or older systems. This can result in a tank full of hot water but none of it reaching your taps.
Bleeding radiators won’t help here you’ll need an engineer to safely clear the blockage or re-balance the system.
5. Failed Heating Element (in Unvented Cylinders)
In systems with an electric immersion heater, the heating element itself may be faulty. If this burns out or breaks, your hot water cylinder won’t heat up, even though the heating is unaffected.
If your system has an immersion heater:
Check for a tripped fuse or breaker
Try the boost switch if it doesn’t heat the water, it could be the element
Again, working with electrics and heating elements is dangerous always leave it to a qualified engineer.
6. Low Boiler Pressure
Boilers need sufficient pressure to function correctly. If the pressure drops too low, it might affect hot water delivery, especially in combi boilers.
Check the boiler pressure gauge:
If it’s below 1 bar, that could be the issue
Only top up the pressure if you know how refer to your boiler manual
Over-pressurising your boiler can damage it. If you’re unsure, call a professional.
Why You Should Avoid DIY Fixes
Boilers and central heating systems are not like changing a light bulb. They contain pressurised water, gas and electrical components all of which can be dangerous if handled incorrectly.
Attempting DIY repairs can:
Invalidate your boiler’s warranty
Lead to leaks or further damage
Risk gas leaks or carbon monoxide exposure
Leave your home without heating and hot water altogether
That’s why it’s always better and safer to let a professional heating engineer handle the issue.
When to Call a Heating Professional
If basic checks don’t resolve the issue and you’re still left with heating but no hot water, it’s time to call in a Gas Safe registered engineer. They have the tools, experience and safety training to diagnose and repair your system efficiently.
At OnSite, we specialise in fast, affordable hot water repairs. Whether it’s a diverter valve, cylinder thermostat, or something more technical, we’ll get your home back to normal quickly and safely.
What We Can Help With:
- Faulty diverter valve replacements
- Boiler diagnostics and pressure checks
- Hot water cylinder thermostat repairs
- Full system inspections and servicing
Get Your Hot Water fixed
If your hot water is not working but the heating is, it’s likely a fault in a specific component like the diverter valve, thermostat, or heating element. While it might be tempting to try fixing it yourself, these systems are complex and risky to tamper with.
Your safest, fastest and most reliable option is to call in the professionals. We’ll diagnose the issue and get your hot water running again without guesswork or risk.
Need Hot Water Repairs? Call the Experts Today
Don’t get stuck without hot water especially when your heating still works. Our qualified heating engineers can quickly diagnose and fix the problem, safely and efficiently. Whether it’s a faulty diverter valve, thermostat issue, or something more complex, we’re here to help.
