What’s Going Wrong & How We Fix It
If your Vaillant boiler isn’t working or your central heating has suddenly stopped heating up, you’re definitely not the only one. We deal with this exact issue for clients every single week and while it can feel stressful or urgent, the cause is usually something we’ve seen a hundred times before. In most cases, it’s completely fixable sometimes with a simple check, and sometimes with a quick repair from an engineer.
In this guide, we’ll walk you through the most common reasons Vaillant boilers stop working, what’s actually happening behind the scenes, what you can safely check yourself, and when it’s time to call us to get everything running smoothly again.
Why Vaillant Boilers Stop Working
Vaillant makes excellent boilers, but like any heating system, parts wear out, pressure drops, and faults appear over time. These are the top issues we’re called out for:
1. Low Boiler Pressure
Probably the most common cause of no heating or no hot water.
Symptoms:
Heating won’t fire up
Error codes like F22
Radiators warm at the bottom but cold at the top
Why it happens:
Small leaks around the system
Bleeding radiators
Expansion vessel problems
Natural pressure loss over time
2. Frozen Condensate Pipe
A big issue in winter.
Symptoms:
Boiler shows an ignition or condensate error
Gurgling noises
Boiler not firing at all
Why it happens:
Cold weather freezes the waste water pipe, stopping the boiler from working as a safety measure.
3. Faulty Diverter Valve
If your hot water works but heating doesn’t (or vice versa), this is often the reason.
Symptoms:
Hot water but no heating
Heating but no hot water
Boiler constantly firing on and off
Why it happens:
The diverter valve gets stuck and can’t redirect hot water where it needs to go.
4. Thermostat or Programmer Issues
Surprisingly common!
Symptoms:
Heating refuses to come on
Heating only comes on sometimes
Temperatures seem incorrect
Why it happens:
Flat batteries
Incorrect settings
Faulty wiring
Thermostat not communicating with the boiler
5. Pump Failure
Your heating pump circulates hot water around the system. When it struggles, so does your heating.
Symptoms:
No heat upstairs
Radiators warm only near the boiler
Boiler overheating or shutting down
Why it happens:
Wear and tear, sludge build-up, or electrical faults.
6. Blocked Heat Exchanger (Sludge Build-Up)
One of the more serious issues we see.
Symptoms:
Loud kettling noises
Boiler cutting out
Lukewarm radiators
Frequent error codes
Why it happens:
Radiators and pipework collect sludge over the years. This causes poor circulation and overheated components.
Checks You Can Try Before Calling an Engineer
There are a few simple, safe checks you can do at home before contacting an engineer. These won’t fix deeper problems, but they can help you rule out easy-to-solve issues.
- Check the Boiler Pressure: It should sit between 1.0 and 1.5 bar. If low, you can top it up using the filling loop instructions are usually inside the boiler manual.
- Reset the Boiler: Sometimes a simple reset clears minor faults. Press the reset button and give the boiler a minute to restart.
- Check the Thermostat : Replace the batteries Make sure the temperature is set higher than the room temp Check Wi-Fi connectivity if it’s a smart thermostat
- Look for Frozen Pipes: If your condensate pipe is frozen, you can pour warm (not boiling) water over it or use a hot water bottle.
- Bleed Radiators: Cold spots mean trapped air. Bleeding them improves circulation and helps pressure stabilise.
If none of this works don’t worry. We fix these issues every day.
When You Should Contact an Engineer Immediately
Some signs indicate a deeper issue that needs urgent attention. If your boiler is repeatedly losing pressure, if you’re seeing regular error codes like F75, F28, or F29, or if the boiler is making loud banging or kettling noises, you’ll want a professional to take a look. Leaks, non-stop cut-outs, and system-wide heating failure also point to a problem that won’t resolve itself.
And of course, if you ever smell gas, switch the boiler off straight away and call for help.
How We Can Help Get Your Vaillant Boiler Working Again
We repair and service Vaillant boilers every day and know exactly how to diagnose these heating faults quickly. Whether it’s a stuck diverter valve, a blocked heat exchanger, a failing pump, or a simple sensor fault, we’ll get to the root of the issue and restore your heating as fast as possible.
We carry replacement parts for all major Vaillant models, and we can handle everything from simple pressure faults to full system cleans. If sludge is the reason your heating isn’t working, we can perform a deep system flush to improve circulation and protect your boiler from future problems.
Most importantly, we explain everything in a clear and friendly way, so you always understand what’s happening and what the repair involves.
Need Your Vaillant Boiler or Central Heating Fixed?
If your Vaillant boiler or central heating still isn’t working, we’re here to help. Whether it’s a complete breakdown or an intermittent fault, our engineers can diagnose the problem, repair it quickly, and get your home warm again.
Call us today for fast, reliable Vaillant boiler repairs or send us a message and we’ll get straight back to you.