Heatline F28 Fault Code: Causes, Fixes & Repair Costs
What does the Heatline F28 fault code mean?
The F28 code on a Heatline boiler signals an ignition lockout. After three unsuccessful attempts to establish a stable flame during the startup sequence, the boiler gives up and shuts itself down. You'll see F28 on the display and the boiler won't fire again until the fault is resolved and the unit is reset. Heatline is part of the Vaillant Group, so the F28 code behaves identically to the equivalent Vaillant ignition fault — causes, diagnostics, and repairs are consistent across both brands.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Gas valve stuck or faulty Common
The gas valve is the most frequently identified culprit when a Gas Safe engineer investigates an F28 on a Heatline boiler. Valves tend to seize in a partially closed position rather than fail outright, which starves the burner of enough gas to sustain ignition. The boiler attempts to light, detects no stable flame, and locks out.
- Worn or dirty ignition electrode or lead Common
The ignition electrode produces the spark that lights the gas, and the flame sensor confirms the flame is present. Over time, electrodes erode, leads crack, and sensor probes accumulate carbon deposits. Any of these prevent reliable spark generation or flame detection, triggering F28 after repeated failed attempts.
- Frozen or blocked condensate pipe Common
During cold spells, the condensate pipe — which carries acidic waste water from the boiler to the drain — can freeze solid where it runs outside. This backs up condensate inside the boiler and can interrupt the startup sequence, causing a lockout that presents as F28. It is one of the few causes a homeowner can fix themselves.
- Insufficient gas supply or supply interruption Sometimes
Low gas pressure at the meter, air trapped in the supply line after work on the pipework, or an empty pre-payment meter can all deprive the boiler of adequate fuel. Check whether other gas appliances in the home — a hob, for instance — are working normally. If they are not, the issue lies upstream of the boiler and requires your gas supplier or a Gas Safe engineer.
- Flue obstruction Sometimes
A blocked or partially obstructed flue terminal can disrupt combustion airflow enough to prevent a stable flame from forming. Debris, bird nesting material, ice, or plant growth around the external flue terminal are all possible causes, particularly in older installations.
- Faulty PCB Rare
The printed circuit board controls the entire ignition sequence. If the PCB develops a fault it may fail to send the correct signals to the gas valve or ignition electrode at the right moment, mimicking symptoms of those individual component failures. PCB faults are less common but possible, especially in older boilers.
How to fix it
- Check that other gas appliances in your home are working DIY safe
Turn on a gas hob burner or check another gas appliance. If it lights and works normally, your gas supply is intact and the problem is specific to the boiler. If nothing gas-powered is working, your supply has been cut or a prepayment meter needs topping up — contact your gas supplier before doing anything else.
- Check for a frozen condensate pipe DIY safe
If the weather is at or below freezing, find where the condensate pipe exits the property — it is usually a white or grey plastic pipe, around 22 mm in diameter, that terminates near a drain or outside wall. If it feels solid or has visible ice, pour warm (not boiling) water along its length to melt the blockage. Once clear, reset the boiler. Consider lagging the pipe with foam insulation to prevent a repeat.
- Inspect the external flue terminal for obvious obstructions DIY safe
From outside (without climbing on anything), check that the flue outlet is not blocked by debris, ice, bird nesting material, or nearby plant growth. If you can safely remove a loose obstruction, do so. Do not attempt to dismantle or alter the flue itself — that requires a Gas Safe engineer.
- Attempt a single boiler reset DIY safe
Locate the reset button or symbol on your boiler's controls (refer to your manual if needed) and hold it for around three seconds. Allow the boiler a full minute to attempt startup. If F28 returns immediately or after a short time, do not reset again — repeated resets without resolving the underlying fault can cause damage and mask the problem from an engineer.
- Have a Gas Safe engineer inspect the ignition electrode and flame sensor Gas Safe engineer
An engineer will check the electrode for erosion and the flame sensor probe for carbon fouling. Cleaning or replacing these components is straightforward for a qualified engineer and is often the quickest fix when the gas supply has been confirmed as adequate.
- Have a Gas Safe engineer test and service the gas valve Gas Safe engineer
The engineer will measure gas pressure across the valve and check for correct operation. A seized or faulty valve will need to be freed, recalibrated, or replaced. This is a gas-carrying component and must only be handled by a registered engineer.
- Have a Gas Safe engineer check the PCB and wiring Gas Safe engineer
If the electrode, gas valve, and supply have all been ruled out, the engineer will inspect control wiring for loose connections, corrosion, or damage, and test the PCB outputs. A faulty PCB will need replacement — it is a higher-cost repair and the engineer may advise you to weigh this against the boiler's age.
- If DIY checks have not resolved the fault, book a Gas Safe registered engineer Gas Safe engineer
An F28 that persists after checking the gas supply, thawing the condensate pipe, and a single reset requires professional diagnosis. Attempting further work on ignition components, gas valves, or the PCB yourself is unsafe and will likely void any remaining warranty. Find an engineer on the Gas Safe Register at gassaferegister.co.uk.
Parts you may need
- Ignition electrode · from £25
- Ignition lead / HT lead · from £20
- Flame sensor / ionisation probe · from £18
- Gas valve · from £120
- PCB (main control board) · from £180
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£320, depending on the underlying cause.
Frequently asked questions
Can I reset a Heatline F28 fault myself?
Yes, one reset is a sensible first step once you have checked the gas supply and ruled out a frozen condensate pipe. Press and hold the reset button as described in your manual. If F28 comes straight back, stop resetting — it will not fix an underlying fault and can make diagnosis harder for an engineer. Limit yourself to two or three attempts at most.
How much does it cost to fix a Heatline F28 fault?
Most F28 repairs land in the £120–£320 range. An ignition electrode or lead replacement including labour typically costs £100–£200, while a gas valve replacement usually comes in around £250–£350 all in. A PCB replacement is a more expensive outlier — often £300–£500 or more depending on parts availability — and if that is the diagnosis on an older boiler, it is worth getting a new boiler quote at the same time to compare.
Why does my Heatline boiler keep showing F28 every winter?
Recurring F28 faults in cold weather almost always point to a condensate pipe that freezes when temperatures drop. The pipe carries waste water outside and is vulnerable to freezing if it is not insulated. The fix is straightforward: thaw it with warm water and then lag the external section with pipe insulation foam from any DIY store. This should prevent the fault returning each winter without needing an engineer.
Is the Heatline F28 code the same as the Vaillant F28?
Effectively yes. Heatline is owned by the Vaillant Group and shares much of the same boiler architecture and fault-code system. F28 means an ignition lockout on both brands, and the causes, diagnostic steps, and repairs are essentially identical. Any Gas Safe engineer familiar with Vaillant boilers will be equally comfortable diagnosing an F28 on a Heatline.