Boiler Fault Guides
Vaillant Boiler Fault Codes Explained: F22, F28, F75 and More
Vaillant boiler fault codes help London householders identify detected conditions; match the full code to your exact model’s manual before deciding what to do next. F75, F22 and F28 do not establish a failed part. If you smell gas, leave and call the National Gas Emergency Service on 0800 111 999. For suspected CO symptoms, get fresh air and call NHS 111, or 999 if serious. See boiler fault codes explained.
Call with your postcode, the boiler make and any fault code showing.
- Gas Safe registered: 648977
- Phone line open 24/7
- Same-day appointments available
Before Any Checks: Gas Smells, CO Alarms and Symptoms
Gas smells, a CO alarm or suspected carbon monoxide exposure mean you must stop troubleshooting.
Smell gas: Avoid flames and electrical switches. Open doors/windows and turn off the gas at the meter only if safe. Leave and call 0800 111 999 from outside before arranging repairs. See HSE gas safety guidance.
CO alarm or symptoms: Get outside into fresh air. For suspected symptoms, call NHS 111, or 999 if serious, then call 0800 111 999. Never delay medical help for a gas call. Treat an alarm as real; carbon monoxide has no smell. See NHS carbon monoxide guidance.
Do not re-enter until advised safe.
Match the Full Display Code to Your Vaillant Model
Record the model and complete displayed code before using a lookup.
Identify
Read paperwork or an accessible external label.
Copy
Record the range and complete model designation.
Photograph
Capture the prefix, punctuation, digits and accompanying text.
Match
Find that appliance’s operating manual.
Never open the boiler casing or work on gas. Check whether the manual identifies a fault or operating status.
Source scope: ecoTEC pro VUW ..6/5-3, installation and maintenance instructions 0020244995_05. This does not establish compatibility with ecoTEC plus 938.
Vaillant Fault-Code Lookup: F75, F22, F28 and Other Codes
Use this lookup only when its model and manual match your boiler; possible causes remain unconfirmed.
F.75 (F75)
Insufficient pressure change at pump startup. Possible sensor, pump, air or water-volume issue. Record the timing.
F.22 (F22)
Low-water-pressure shutdown. Water shortage is possible. Compare your reading with the manual and.
F.28 (F28)
Startup ignition failed. Possible supply, ignition or condensate-route issue. Report known supply interruptions.
F.29 (F29)
Re-ignition failed during operation. Supply interruption is possible. Record what was running.
F.20
Temperature-limiter shutdown. Sensor contact or air may contribute. Arrange assessment.
F.23
Excessive temperature difference. Poor circulation may contribute. Report heating symptoms.
F.24
Temperature rises too quickly. Air or insufficient water may contribute. Arrange assessment.
F.27
Incorrect flame detection. Electrode or electronics issues are possible. Arrange assessment.
F.32
Fan-related fault. Fan or connection problems are possible. Arrange assessment.
F54
Not established by this source. Obtain model-specific assessment.
F.61
Gas-valve actuation fault. Wiring, valve or electronics may be involved. Arrange assessment.
F.62
Delayed gas-valve switch-off. Valve or electronics may be involved. Arrange assessment.
F.70
Invalid appliance identification/configuration. Coding issues are possible. Report recent repairs.
F.72
Excessive difference between flow/return sensor readings. Sensor function or contact may contribute. Arrange assessment.
F76
Not established by this source. Obtain model-specific assessment.
F.83
Insufficient difference between flow/return temperature readings. Sensor contact or water volume may contribute. Arrange assessment.
Scope: The ecoTEC pro manual above supports every defined entry below. Some listed codes may not appear on every covered appliance. For every entry, record the display; internal testing and repairs require an engineer.
Source: Vaillant ecoTEC pro instructions 0020244995_05, Appendix D, pages 46–48. Source checked: 1 November 2026.
Verify: check against the manufacturer's manual
For help, see Vaillant boiler repairs.
Vaillant F75: Does the Code Prove the Pump Has Failed?
F75 does not prove pump failure on the cited ecoTEC pro models.
Display condition
The expected pressure change was not detected when the pump started.
Observations
Record the model, full code, visible pressure and timing.
Diagnosis
An engineer distinguishes pump performance from sensor, air or water-volume problems.
Do not buy parts from the code alone or attempt pump freeing, sensor cleaning or internal venting.
Vaillant Boiler F22: What to Check Before Adding Water
F22 reports a low-water-pressure shutdown on the cited models; compare the reading with your operating instructions before adding water.
Below the specified cold range
Top up only if your matching manual permits it and you can identify the correct filling arrangement.
Normal, high or unclear
Do not add water; arrange assessment.
Falls again after a permitted top-up
Read why a boiler keeps losing pressure and arrange investigation. Repeated filling is not a repair.
Never operate the pressure relief valve to correct a reading or attempt expansion-vessel work.
Vaillant F28: What an Ignition Fault Tells You
F28 means startup ignition failed on the cited models, but does not identify the responsible component.
Vaillant F29: Why Losing the Flame Is a Different Condition
F29 concerns unsuccessful re-ignition during operation on the cited models.
- F28: Ignition fails during startup.
- F29: Re-ignition fails during operation.
Report whether heating or hot water was running before shutdown. The code does not prove a gas leak or justify repeated resets.
You can report: An existing meter message or known supply interruption.
Engineer-only work: Testing ignition, flame sensing, gas controls and internal condensate routes. Do not light another appliance as a diagnostic test. Gas smells or CO concerns require emergency action first.
Other Vaillant Codes: Read the Condition Before Naming a Part
Other codes also need model-specific interpretation before a component can be blamed. These groups explain the lookup’s limits.
F20, F23 and F24: Temperature and Circulation Readings
These describe separate conditions: temperature-limit shutdown, excessive temperature spread and excessively rapid temperature rise respectively. Record what happened before shutdown. Sensor readings do not establish pump failure or a need for flushing. Stop before internal bleeding or adjustments.
F27, F32, F54, F61 and F62: Where Homeowner Checks Stop
Internal flame, fan, electrical and gas-control checks require an appropriately qualified engineer. For the cited models, F27 concerns flame detection, F32 the fan, F61 valve actuation and F62 valve switch-off. F54 remains undefined here. Record accompanying messages; do not access wiring, gas settings or safety devices.
F70, F72, F76 and F83: Model Details Matter
Match the appliance before interpreting configuration or sensor messages. The cited source covers F70 configuration, F72 sensor-temperature difference and F83 temperature response; it does not establish F76. Report whether the message followed servicing or repair without assuming causation. Leave service menus and sensor positioning to an engineer.
Safe Checks and the Limit on Resetting
Use only checks allowed by your operating manual, and stop if the fault persists or returns.
After excluding gas/CO warnings, record the display and pressure, check user-level thermostat/programmer settings and note known power or supply interruptions.
Reset limit: Attempt a reset only if your exact manual permits it for that condition. Limit this to one attempt. If the fault remains or returns, stop. If instructions cannot be matched, do not improvise.
When to Call an Engineer About a Vaillant Fault
Arrange assessment when safe user checks end or a fault needs internal investigation.
Stop for:
- Recurring lockout.
- Repeated pressure loss.
- An unexplained normal/high reading alongside a fault.
- A code requiring internal tests.
- Instructions that do not match your appliance.
Arrange professional boiler fault diagnosis so the cause can be established before work is recommended.
Have your model, full code, pressure reading, heating/hot-water symptoms, timing and actions already taken ready.
Boiler repair, servicing and gas work
Arrange Help With a Vaillant Boiler Fault in London
Call All Service 4 U to discuss a Vaillant boiler fault in London with your model and full code ready.
Call us 24 hours a day, 7 days a week. Give your postcode, symptoms and observations. Our Gas Safe registered engineers assess the fault before recommending work. Business registration: 648977.
Discuss My Vaillant Boiler Fault: 020 3740 6785
020 3740 6785
Frequently Asked Questions
What Does the F35 Fault Code Mean on a Vaillant Boiler?
F35 needs an exact model and applicable fault table before it can be interpreted reliably. The cited ecoTEC pro appendix does not establish its meaning. Record the complete display, model designation and manual details, then arrange assessment rather than borrowing a definition from another range.
How Can I Tell Whether My Vaillant Boiler Is On?
A lit display alone does not show that the boiler is heating. Powered means controls have power; standby means waiting; active demand means heating or hot water has been requested. Check your operating manual’s indicators and user controls. Do not treat fault and status messages as interchangeable.
What Does the Vaillant F84 Error Code Mean?
For the cited ecoTEC pro models, F84 concerns an implausible temperature difference between sensors. It does not establish which component has failed. Record the full code and model for assessment. Do not move sensors, disconnect wiring or order replacement parts based on the display alone.
What Does the Vaillant F71 Boiler Fault Code Mean?
For the cited ecoTEC pro models, F71 concerns an implausible flow-temperature sensor reading. A reported reading is different from a tested component failure. Give the engineer the complete code and model designation. Sensor checks and any work inside the casing belong to the engineer.
Why Is There No Hot Water If My Vaillant Shows No Fault Code?
No hot water without a code still needs assessment; the missing code does not identify the cause. Report whether heating works and whether every hot tap is affected. Limit checks to user controls and your operating instructions. Boiler type matters, so do not assume a combi-specific component is responsible.
How Do I Check the Engineer Is Qualified to Work on My Boiler?
Check the attending engineer’s Gas Safe ID and current qualifications for your boiler’s gas work. Confirm their identity, card validity and relevant appliance categories against the Register. A business registration number alone does not establish the qualifications of the individual arriving to carry out the work.
Still have a question or need urgent assistance? Call 020 3740 6785, tell us what has happened and we will tell you what happens next.