Vaillant Error Codes & Diagnostics
Complete diagnostic directory for official Vaillant fault codes. Verify root causes, safe troubleshooting steps, and replacement part numbers before calling a technician.
Vaillant ecoTEC F.22 fault code: low water pressure explained
Vaillant assigns F.22 to low water pressure in the sealed heating circuit, and the boiler stops firing to protect itself from running dry. Vaillant names the normal range as 1 to 1.5 bar, and lists a faulty pressure sensor, loose sensor or pump wiring, and a failed internal expansion vessel alongside a genuine water shortage. Applies to: Vaillant ecoTEC plus and ecoTEC sustain boilers that list F.22 This meaning follows the Vaillant United Kingdom fault-code list for ecoTEC boilers that display F.22. Other Vaillant ranges and the same code on another appliance can be mapped differently, so confirm the model from the data badge before you top up or reset. Owner-safe checks: Read the pressure gauge with the system cold, and top up to about 1.5 bar with the filling loop only if it is below 1 bar, then close both valves fully. | Record how many times the pressure has needed topping up in the last month and whether it drops fastest hot or cold. Qualified technician: A repeated pressure loss, a suspected leak, an expansion vessel check, or any sensor or wiring inspection inside the boiler casing needs a Vaillant or Gas Safe registered engineer.
Vaillant F.23: the temperature spread says water is barely moving
Vaillant defines F.23 as the temperature spread being too great, or water circulation too low. The boiler measures flow and return temperature and compares them, and when the difference grows beyond what the appliance allows, it concludes that not enough water is passing through the heat exchanger to carry the heat away. Applies to: Vaillant ecoTEC gas boilers covered by the Vaillant United Kingdom fault code list The definition used here is Vaillant's own fault code list for ecoTEC appliances sold in the United Kingdom. Vaillant uses different fault numbering on other ranges and in other markets, and a Glow-worm appliance, though part of the same group, has its own published list. Check the code against the label inside your own casing flap. Owner-safe checks: Feel each radiator after a heating attempt and note which get warm, which stay cold, and whether the cold ones are cold at the top or the bottom. | Check the pressure gauge and record the reading, since a system that has lost water often has air in its place. | Confirm that radiator valves and any thermostatic heads have not been closed off, particularly on circuits recently worked on. Qualified technician: Setting or replacing a pump, venting a sealed primary circuit, power flushing, and testing flow and return sensors are Gas Safe registered tasks on this appliance. | Kettling or banging from the boiler is a reason to stop using the heating rather than to keep trying, because boiling against the exchanger causes cumulative damage.
Vaillant F.28 and F.29: two ignition faults with one owner check
Vaillant defines F.28 as the flame signal not being detected during the ignition phase, and F.29 as an unsuccessful re-ignition after a flame loss during operation. The codes describe when the flame went missing, not what removed it, and Vaillant lists insufficient gas, a blocked condensate pipe, and a faulty ignition electrode among the causes of both. Applies to: Vaillant ecoTEC gas boilers covered by the published United Kingdom fault code list These meanings come from Vaillant's own United Kingdom fault code list for its gas boilers and are written with a full stop between the letter and the number. Other manufacturers use F28 and F29 for entirely different conditions, and a code read from a non-Vaillant appliance does not carry these definitions. Owner-safe checks: Check whether other gas appliances in the property work and whether a prepayment meter has credit. | Look and listen for a gurgling or bubbling sound at the boiler or the external condensate pipe. | Thaw an accessible frozen condensate pipe with warm, not boiling, water poured along its length. | Reset the boiler once according to its own manual after the condensate pipe has drained. | Insulate the condensate pipe afterwards, as Vaillant recommends, to reduce the chance of a repeat. Qualified technician: The same code returning after one reset with the gas supply confirmed and the condensate pipe clear. | Any suspicion of an ignition electrode, gas valve, flue, or circuit board fault, all of which need the casing opened. | A condensate pipe that is not reachable from ground level. | F.54 shown alongside F.28 or F.29, which Vaillant attributes to the gas supply. | The smell of gas, which takes priority over every code on this page and is answered by evacuating and dialling 0800 111 999.
Vaillant F.32: no fan means no combustion, by design
Vaillant gives F.32 as the fan being faulty or not connected. On a room-sealed condensing boiler the fan is what draws combustion air in and pushes flue gases out, so the appliance cannot burn gas safely without it. The lockout is not the boiler being cautious; it is the only acceptable response to losing forced draught. Applies to: Vaillant ecoTEC gas boilers covered by the Vaillant United Kingdom fault code list This definition comes from Vaillant's fault code list for ecoTEC appliances in the United Kingdom. The same number means something else on other manufacturers and on some Vaillant ranges outside the ecoTEC family, so read it against the list printed inside the casing flap of your own boiler. Owner-safe checks: Listen at the start of an attempt and note whether any fan sound occurs at all, and whether it sounds as it used to. | Record the exact code and how many attempts produce the same result before you stop trying. | Check whether any recent service, part replacement, or electrical work preceded the fault. Qualified technician: Testing, cleaning, or replacing a boiler fan and its wiring is Gas Safe registered work on a sealed combustion appliance in the United Kingdom. | Resist the urge to take the front panel off for a look. On a room-sealed appliance that panel is a safety component, and opening it breaks the separation it exists to maintain.
Vaillant ecoTEC plus F.75: pressure rise not detected
On the documented Vaillant ecoTEC plus, F.75 means the control did not detect sufficient heating-water pressure change when the pump started. The service list includes low fill pressure, air or insufficient water, expansion-vessel influence, pump or pressure-sensor faults, and their wiring; neither component is proven by the code. Applies to: Current ecoTEC plus boilers covered by manual 0020308121-04 This meaning follows current ecoTEC plus installation and maintenance instructions 0020308121-04. Older ecoTEC generations, commercial boilers, aroTHERM heat pumps, and regional variants require their own document. Owner-safe checks: Photograph F.75 and the visible pressure, note recent bleeding or filling, and inspect only accessible external pipework for water. Qualified technician: Pump, pressure-sensor, expansion-vessel, filling, venting, internal leak, wiring, gas, and sealed-case work requires a qualified heating engineer.