Skip to content

Boiler Not Working? Guide to Heating System Solutions

Picture of sid


You get home from work on an icy winter night and run straight to the shower. You turn on the tap, hankering with excitement for the first touch of hot water to warm your frozen body. Instead, you are hit with water as cold as the rain outside. What do you do when you have no hot water or heating? Our property management team at Flex Living fix boiler problems every day, so here’s our best advice on what to do when your boiler stops working.


In this article, we’ll cover the two most common systems for hot water and heating: Gas Combination Boilers and Electric Immersion Heaters. Gas Combi boilers are relatively small boiler systems that provide both hot water and central heating in the same system. On the other hand, electric immersion heaters use electricity and heating elements to heat the water inside and supply hot water instantaneously. For a more in-depth look at gas and electric heating systems, read our electric vs gas central heating blog.

In this article, we are going to discuss :

What Do Gas Boiler Error Codes Mean?

By knowing what each error code means, you can then try and fix your gas boiler, or at least call a professional for a quicker, more efficient repair. If you have problems with your immersion heater, skip to the section on ‘How to Fix Common Immersion System Problems’.

Below is a list of common codes for some of the most popular boiler systems including:

  • Vaillant
  • Baxi
  • Ideal
  • Worcester BOSCH
  • Viessmann
  • Glow-Worm
  • Potterton

Note: the fault code may vary depending on which model of boiler you have within each system. If you cannot find the code you’re looking for, consult the manufacturers manual.

Possible System Error Codes for Gas Combination Boilers

Common ProblemVaillantBaxiIdealWorcesterViessmannGlow-WormPotterton
Low pressureF22E.02-.07F11017W
Pressure gauge reading lower than 1 barF22E118, E119
Boiler or radiator leaksF22H.02-.06F1, L-AA1, EA 227Pressure gauge reading lower than 1 barF22E119
Frozen or blocked condensate pipeF28, F29E28L2, F2D5F4 EEF1, F4, F28, F29E133
Ignition failF28, F29E133 or 3 red flashesL2, L-FEA227F5F28E128, E133
Expansion vesselF75E117, E118, E119F1A1, EA 227F0
PCB faultF92, F27, F28, F29, F33, F61, F62H.02-.02
H.03 -.01
E.02 - .16
E.02 - .17
F9F7, 224FEF11, F13E131, E151, E152
Heat exchangerF76, F80E433, E13L92963 B
2964 B
966 B
Pressure sensorF72, F73, F74, F75E78, E164F61017W, 1065BF0F9E78
OverheatingF20E110, E131L9, H9, HA, LA, L-AE5 218
E5 332
E9 219
E9 224
D1 286
60, 68, 70, 78, BD, BE, BFF20E125, E131
Fan faultF32E.01 – .11, E.04 – .13
E160 or 4 red flashes
C7 214
C6 215
C6 216
C7 217
C1 264
F-FAF3E160, E161
Noisy boilerF20E110, H.02-.06L2, L-FA41A8F9E110
Thermostat signalF5E.04 - .08, E110, E130, E20C0, F5A21F2

How to Fix Common Gas Boiler Problems

To find out what is wrong with your boiler, you can:


  • Check system-specific fault codes
  • Look for visible defects or;
  • Contact a Gas Safety heating engineer

Below is a list of possible solutions if your boiler stopped working. Remember to always consult your manufacturer’s instruction manual for more information before taking any action.

Problems with Pressure

Problems relating to pressure are a primary cause of hot water and heating loss in the home. Pressure issues can result from a number of things: 


  • Topping up the pressure
  • An issue with the pressure relief valve
  • A torn expansion vessel
  • Leak in the system
  • Faulty pressure Sensor
  • Faulty PCB

Topping Up the Pressure (Repressurising)

Your boiler needs stable water pressure to circulate water efficiently around the home. You can check the pressure by looking at the boiler’s gauge. On most digital gauges, you can see if pressure is too high or too low through the flashing pressure reading. If your digital gauge shows pressure at less than one bar, this usually signifies low pressure. Sub-optimal pressure means the boiler system must work harder to heat your property, which involves higher energy consumption and thus higher costs. So it’s in your best interest to take action to restore your boiler’s pressure.   Low boiler pressure can occur over time as a system gets older, but if the pressure keeps dropping repeatedly, you may need to repressurise the boiler system by following these steps: 1. Switch off boiler and let cool 2. Ensure the filling loop (pipe that connects boiler to mains water supply) is firmly attached at both ends 3. Open the valves at both ends to allow water to flow in and fill the boiler 4. Allow the pressure gauge to rise to 1-1.5 5. Turn off both valves of filling loop 6. Switch boiler back on 7. If you notice the pressure continues dropping on your boiler there could be a leak (go to the system leak section). 8. If you notice the pressure gauge increasing quickly and above a pressure level of 3, then you could have a faulty expansion vessel (go to the torn expansion vessel section).
a boiler system

Issue with Pressure Relief Valve

pressure relief valve parts

To fix a leaking pressure relief valve, you should hire a Gas-Safe engineer, who will most likely follow these steps:


1. Ensure boiler is turned off

2. Close off fill valve that supplies water to the system

3. Wait a couple of hours for boiler to cool

4. Drain water from boiler system

5. Open the drain valve and watch the pressure gauge 

6. When pressure reaches zero, close the valve

7. Use a wrench to remove the pressure relief valve from the boiler

8. Wrap Teflon tape around around all but the bottom two threads of your new replacement pressure relief valve

9. Screw the new valve onto the boiler and tighten with a pipe wrench

10. Open the value to refill the system with water 

11. Bleed any air out of the system by opening the bleed valves on your radiators.


Keep in mind that you should be replacing your pressure relief valve every 4-5 years. To prevent future leaks, call a Gas-Safe Engineer to service your boiler.  You can watch a tutorial on how to replace a pressure relief valve yourself here.

Torn Expansion Vessel

torn expansion vessel parts

Sometimes, a faulty expansion vessel may only need a simple repressurising process to be fixed. To repressurise your boiler, follow the steps above.


The best way to check if there is a fault with your expansion vessel is to check the pressure gauge:   


  • When turning on the central heating with a target temperature of 25 degrees celsius or more, the pressure gauge will rapidly fluctuate between a normal pressure (1-1.5) and an abnormally high pressure (2.5+).  


There are other checks to diagnose a problem with the expansion vessel, but these should be done by a Gas-Safe engineer. These checks include:


  • Taking the cap off the expansion vessel to see if the valve is wet (seeping water could indicate a tear in the vessel) 
  • Using a pump to re-pressurise the expansion vessel and then see if it holds the pressure stably or if the pressure drops significantly. If the pressure drops by more than 10%, there is likely a tear in the vessel.


Replacing an expansion vessel requires the use of a Gas-Safe engineer, but here are the basic steps involved:


1. Buy a new vessel (make sure it’s the same brand as your boiler)

2. Turn off boiler system and stop the water supply

3. Wait a couple hours for the boiler to cool 

4. Open the drain valve and let water exit to boiler 

5. Detach the old expansion vessel (try not to damage other piping work or components in the process)

6. Check that the new vessel is set to a normal pressure level

7. Use Teflon tape to tape the connectors and then install the new vessel 

8. Turn on water supply and reconnect the power supply

9. Once the boiler is heated, turn on a hot water tap and check for heat.


See a video tutorial on how to change a faulty expansion pack here. Note that this video refers to a Worcester Bosch Greenstar Combi Boiler, it may be easier to follow steps if you search for a tutorial specific to your boiler system and model.

Leak in the System

You can usually tell that your boiler system is leaking if the pressure reading keeps dropping even after you’ve topped it up. If this happens, turn off the electricity supply before investigating to reduce the risk of further damaging your heating system. Try and diagnose where the leak is coming from. If water is coming from the pressure relief valve, this could indicate that the boiler pressure is too high, and the valve is releasing some water to reduce the pressure. For information on repairing a pressure relief valve, see the above section under ‘Issue with Pressure Relief Valve’. Alternatively, the leak could be coming from elsewhere in the system (a common leaking point is a valve on one of your radiators). Check the radiators around your property for any wet patches on the floor or slow drips (these leaks could be causing the pressure to drop). Ensure the heating system has cooled down completely before you tighten any radiator valves.  If you find a leak and are not sure how to fix it, turn off the system and call a Gas-Safe engineer. 
a. Faulty Pressure Sensor
faulty pressure sensor

You will need to hire a Gas-Safe engineer to inspect and potentially repair or replace your pressure sensor. A Gas-Safe engineer will:


1. Switch off the electricity

2. Close the gas valve

3. Remove the enclosure panel 

4. Drain heating water from the boiler

5. Flip down the control console

6. Disconnect wires from the existing water pressure sensor 

7. Pull off the locking clip and detach the existing water pressure sensor 

8. Insert new pressure sensor and attach locking clip

9. Reassemble the boiler

10. Fill the boiler with water, flush and check for leaks.

PCB Fault

A PCB (printed circuit board) fault may be behind many error codes. Your boiler system might show error codes related to problems with low boiler pressure, ignition failure or pressure sensor issues, when actually the real underlying problem is the PCB. This is because the PCB is the boiler’s electronic interface, so if the wiring is faulty or the circuit board stops working, random codes may appear. As a result, it can be hard to identify whether a PCB needs replacing as opposed to what another error code might suggest. However, there are some ways to identify a faulty PCB.  


If there is a problem with the Printed Circuit Board (PCB), you might notice the following:


  • A burning smell
  • No power
  • Wiring issues
  • Sporadic operation (including constantly changing error codes)


If you suspect a faulty PCB, it is best to call a Gas-Safe engineer to investigate further and repair the issue. If you require replacement services, new PCBs are quite expensive. You can, however, buy refurbished PCBs second hand at a more reasonable price.

Thermostat Signal Issues

If your boiler is not responding to your thermostat, there are four things you can do:


1. Replace the thermostat batteries

2. Relocate your thermostat closer to the boiler

3.Opt for a Smart Thermostat

4. Call a Gas-Safe engineer if you still cannot fix the problem

Frozen or Blocked Condensate Pipe

Boiler pipes can become frozen in winter, or built-up sludge can block the condensate trap, which can cause the system to shut down. 


The best way to fix a frozen pipe is to use a defrosting method (you shouldn’t need to call a Gas-Safe engineer for this). To thaw a frozen pipe, follow these steps:


  1. Locate the condensate pipe: The condensate pipe is a small, often white, plastic pipe that sticks out from the bottom of your boiler and usually runs into a drain under a sink or is routed through the wall into an external drain. If you have a frozen condensate pipe, you will likely hear gurgling sounds from your heating system.
  2. Defrost the pipe: Use a hot water bottle or microwaveable heating pack to melt the blockage. You can also pour warm water onto the pipe.
  3. Restart the boiler: Once you have cleared the blockage, restart the boiler (consult the boiler manual if unsure how to do this).


To prevent the condensate pipe from freezing in the future, you can get a Gas-Safe engineer to re-install the condensate pipe so that it runs internally (rather than externally) and is therefore less likely to freeze.


If the condensate trap is blocked due to sludge (a deposit of minerals, oils and other matter that accumulate in the boiler tank over time), it’s best to call a Gas-Safe engineer to flush the system with an inhibitor and install a magnetic filter to catch heating sludge. If left untreated, a buildup of sludge can cause your whole boiler system to stop working, so make sure you get on top of it early!

Noisy Boiler

Noises coming from your boiler can range from whistling and humming sounds to loud bangs. It’s important to check a noisy boiler because over time, vibrations can damage wiring and connections inside the system. Some common causes and solutions to a noisy boiler include the following:


1. Limescale buildup in pipes – Call a Gas-Safe engineer to flush the system out then fit a limescale reducer.

2. Sludge buildup – Call a Gas-Safe engineer to flush the system with an inhibitor and install a magnetic filter to catch heating sludge. To avoid build up of sludge and limescale, get your boiler serviced regularly and ask your Gas-Safe engineer to clear the system.

3. Low water pressure – Fix the water pressure by repressurising the boiler system (see steps above under ‘No Pressure in Gas Boiler’).

4. Airlock in boiler pump – If the pump contains a bleed screw, you can release the air from the pump. Otherwise, call a Gas-Safe engineer.

Overheating Boiler

Your boiler may be overheating because of the following:
  • Limescale buildup
  • Blockage (sludge)
  • A faulty thermostat 
  • Banging noises indicating a faulty heat pump
For limescale buildup and sludge blockage, refer to the sections on Limescale and Frozen or blocked condensate pipes. If you suspect a faulty thermostat to be the issue, see the section on Thermostat signalling issues. If you suspect a faulty heat pump is the issue, call a Gas-Safe engineer to repair or replace the pump.

Gas Boiler Not Firing Up (No Pilot Light)

If there is no pilot light on the boiler or it keeps going out, you will not get any heating or hot water. The pilot light is used to ignite the gas that heats the water in your boiler and catalyses your central heating.


First, check that there is a functioning gas supply to your property:


1. If you have a gas cooker in the kitchen, simply turn on the cooker and check that it is working. If it works, then your gas supply is functioning properly. 

2. If you don’t have a gas cooker, check the gas metre.

3. Ensure the shut off valve on your gas metre has not been accidentally closed or nudged. Even a slight nudge moving the valve into a partially closed position can be enough to cause ignition failures in the boiler. 

4. If you have a smart metre, ensure that the metre status is set to ‘Credit ON’. 

5. If your metre’s status is ‘Credit OFF’ follow these steps to reset your gas metre.

6. If you have a pay as you go metre, ensure the credit is positive (otherwise the metre will automatically close the gas supply).


Assuming your gas supply is all good and functioning, then get a Gas-Safe engineer to check the following things to fix your pilot light:


1. Check for draughts coming from poorly sealed windows or under doors that could be blowing out the pilot light.

2. Use the manufacturer’s instruction manual to locate the pilot light valve screw. Adjust the screw until the flame turns blue.

3. If the above does not fix the problem, call a Gas-Safe engineer to determine whether there is a problem with the thermocouple (the sensor that opens the gas valve when the pilot light is ignited).

Fan Issue

If your fan speed is too low, call a Gas-Safe engineer to adjust the fan speed and reset the boiler.


Loose connections or wiring on the fan prevent signals from reaching the PCB, which causes the boiler to lock out. To fix fan wiring issues, get a Gas-Safe engineer to secure any loose connections and check the fan works afterwards.

Faulty Heat Exchanger

faulty heat exhanger

The first sign of a faulty heat exchanger is leaking. You’ll see water dripping from underneath your boiler. Other common signs of heat exchanger problems include:


  • Loud noises
  • Locking out
  • Limescale buildup
  • Central heating sludge 


A faulty heat exchanger is not a DIY job; it’s best to call a Gas-Safe engineer to further investigate and repair any damage or replace the component. 

How to Fix Common Electric Immersion System Problems

An immersion system is an electric heating system that contains heating elements to warm the water inside. People often use immersion heaters as primary heaters or backup water heaters for properties that already use a boiler system. For more information on electric heating systems, read our electric vs gas central heating article.

First: Check the Programmer

Before trying to fix anything, check that the boiler programmer is turned on. If it’s turned on and the hot water is still not working, try pressing the ‘boost’ button or reconfiguring your system’s programme to heat water to your desired schedule (unlike combi boilers, immersion heaters need to be reheated after use; your system programmer can be set to a certain schedule so it  reheats after use automatically). 

Tripped Circuit Breaker

If there is no power supply to the programmer, check the electrical consumer unit – you could have a tripped circuit or a blown fuse. This can occur when the electrical circuit trips to avoid overheating and causing extensive damage to the entire circuit.     


If you have reset the circuit breaker on your consumer unit and still have no power supply, check the fuse (usually located in a socket close to the boiler programmer with the word ‘Fuse’ on the switch and an orange light). If the fuse has blown and the circuit breaker is on, the fuse light will not be lit, even when the fuse switch is on. In some cases, there is no light and you need to use a voltage tester to check for power. Before replacing a fuse, always ensure that you turn off the power supply from the consumer unit first. We recommend enlisting the help of a professional. 


If the system keeps tripping or the fuse keeps blowing, you may have a leak somewhere causing the circuit to break, or you may have a fault in the heating element.

Damaged Heating Element

If the programmer has been on for a few hours with a light or ‘on’ signal indicating that the water is heating up, and you have tried resetting the thermostat but still have no or very little hot water, you could have a faulty heating element. Damage can occur to the immersion heating element over time (i.e., rust or limescale buildup). This can cause slow heating of water and can also cause the heater to turn on and off suddenly. To fix this problem, it is best to call a plumbing professional to clean the heater and test or replace the heating element.

Faulty Thermostat

If your programmer is definitely on and your system has been running for a couple hours with no hot water, check the thermostat. You can reset most modern systems with external thermostats by pressing a reset button. For an older system, follow these steps:


  • Turn the circuit breaker off to cut the power to your immersion heater
  • Remove the plastic safety lid – do not touch the wires
  • Press the small ‘reset’ button (you may need a small needle or pin to reach the switch)
  • Put safety cover back on
  • Turn on power and test the heater
faulty thermostat

Limescale Build-Up

Limescale occurs when calcium and magnesium minerals in hard water settle and build-up in appliances. As with other electric heating systems, limescale is always a possibility and increases the need for maintenance and repairs on these systems.


A professional can take apart the heater and use a higher-pressure water stream to flush out the limescale. For a more long-term solution, ask a professional to install a limescale-preventing filter into your heating system.

Insulation Breakdown

Over time, temperature, pollutants like limescale and electrical pressures can cause an insulation breakdown. This can stop the electrical current flow from passing through the heating element efficiently. In turn, the system can become overloaded, damaging wires or tripping circuit breakers. To prevent this from happening, it’s best to call a professional to examine the immersion heater and see if any parts need repairing or replacing.

Hot Water Runs Out Quickly

If your system starts releasing hot water but it comes in short bouts and runs out quickly, you may need to repressurise the immersion heater (if it is an unvented cylinder). To do this, follow these steps:


1. Allow cylinder to cool by turning off any immersion heaters to the cylinder 

2. Drain all hot water out of the cylinder by opening the lowest hot tap in the property 

3. Turn off the mains supply to the unvented cylinder

4. Open the lowest hot tap in the property

5. Hold open the temperature and pressure relief valve until the water stops running from the lowest open tap

6. Close temperature and pressure relief valve and open the mains cold water supply to the cylinder

7. When normal water flow and pressure returns to the lowest open tap, close the tap

8. Turn immersion heater back on


If water keeps dripping near the pressure relief valve, you will need to employ a heating engineer to check your hot water system properly.

Stress-Free Boiler Maintenance with Flex Living

Does this all sound a bit overwhelming? Why not rent your property with Flex Living so you don’t have to worry about the hassle of all these repairs and maintenance issues!

Most traditional property companies charge hefty management and maintenance fees for the inclusion of these services. But we are different at Flex Living. We don’t charge our landlords a single pound for our management services, and we offer free maintenance callouts so you don’t amass hidden costs. Get in touch with us today to discover more about our cost-saving property management services.


Please note: The information in this article should be used for general guidance only. Always consult the manufacturer’s manual or discuss with a qualified professional before commencing any work.

Have any questions? Let's chat!

Get our monthly updates in the BTL market

Are you a landlord ?

Join over 72,000 brilliant UK landlords

Stay up to date with the latest changes in the buy to let market, topics include new regulations, cladding, rental market changes, new rules…

Have any questions? Let's chat!

We're committed to your privacy. HubSpot uses the information you provide to us to contact you about our relevant content, products, and services. You may unsubscribe from these communications at any time. For more information, check out our Privacy Policy.