Faults · repairs by RGI engineers
Boiler error codes
What the common codes on Vaillant, Ideal and Baxi boilers mean, from the makers' own pages: which ones you can clear yourself, and which need an engineer.
- From the makers' own guidance
- Safe checks first
- Price before anything is booked
A fault code is the boiler telling you which part of its start-up failed. The same few causes sit behind most of them: low water pressure, no gas reaching the burner, a frozen condensate pipe, or a sensor fault. The first three you can check yourself. A sensor, a fan, a PCB or anything inside the casing is an engineer's job.
Below are the codes the makers themselves publish for the brands most common in Dublin homes: Vaillant, Ideal and Baxi. Each line is from the maker's own page, read 29 October 2026.
The common codes, from the makers
| Make | Code | What it means | What to do first | Causes the maker lists |
|---|---|---|---|---|
| Vaillant | F.22 | Low water pressure | Top up to 1–1.5 bar. If it shows more than 1 bar and still faults: engineer | Pressure, sensor, wiring, expansion vessel |
| Vaillant | F.75 | Pressure change too low when the pump starts | Top up to 1–1.5 bar. Still faulting: engineer | Pressure, air, sensor, pump |
| Vaillant | F.20 | Safety cut-out operated | Engineer or installer | Low pressure, sensor, circulation fault |
| Vaillant | F.28 | No flame at ignition | Check other gas appliances, prepayment credit, frozen condensate pipe. Then engineer | Gas supply, condensate, electrode, PCB, flue |
| Vaillant | F.29 | Flame lost during operation, re-ignition failed | Same checks as F.28. Then engineer | Gas supply, flue, earthing, condensate |
| Vaillant | F.12 / F.13 | Hot water or cylinder sensor short-circuited | Engineer | Sensor or its wiring |
| Ideal | F1 | Low water pressure | Check the gauge: 1–1.5 bar. Top up and restart | Pressure |
| Ideal | F2 | Flame loss | Check other gas appliances, the meter, prepayment credit. Then Ideal or an engineer | Gas supply |
| Ideal | L2 | Ignition lockout | Check the condensate pipe, then the gas supply. Then Ideal or an engineer | Condensate, gas supply |
| Baxi | E28, E53, E133, E119, E128 | Boiler shut down | Thaw the condensate pipe with warm water or a hot water bottle, never boiling water. Reset | Frozen condensate pipe, among others |
Sources: Vaillant boiler fault codes; Ideal Heating, Logic System troubleshooting; Baxi, error codes E23, E53, E133, E119 and E128. All read 29 October 2026. Codes differ by model: check your own boiler's manual, and never open the casing.
Low pressure codes: F.22, F.75, F1
Vaillant lists "the water pressure in your system is below the normal range of 1 to 1.5 bar" first among the causes of F.22, then a pressure sensor fault, loose wiring and a faulty expansion vessel. Its guidance says that if the gauge shows under 1 bar, topping up through the filling loop "can be solved without an engineer if you are competent to do so", and if it shows more than 1 bar the fault is for an engineer (Vaillant). Ideal's F1 is the same fault: check the gauge for 1 to 1.5 bar, top up, restart (Ideal). If the code comes back within days, read boiler losing pressure: the top-up isn't the fix.
No flame codes: F.28, F.29, F2, L2
These mean the boiler tried to light and couldn't, or lost the flame and couldn't relight. Vaillant's list of causes for F.28 starts with "not enough gas reaching the boiler (for example, low gas pressure or insufficient credit on a pre-payment meter)", then "condensate has backed up in the combustion chamber due to a blocked condensate pipe", then the ignition electrode, the PCB and the flue. Its first steps: check if other gas appliances work, check prepayment credit, and in cold weather check for ice in outdoor condensate pipes. Ideal's L2 guidance is the same: condensate pipe first, then whether other gas appliances work, then the meter and credit. If the hob doesn't light either, the fault is the gas supply, not the boiler: ring your gas supplier, or if you smell gas, Gas Networks Ireland on 1800 20 50 50 from outside (Gas Networks Ireland).
The frozen condensate pipe: E133 and friends
A condensing boiler drains acidic water through a small plastic pipe, often to an outside drain. In a frost it freezes, the water backs up and the boiler shuts down. Baxi says a boiler showing E28, E53, E133, E119 or E128 "may" have a frozen condensate pipe, and tells you to warm the exposed length "using either a hot water bottle, a microwaveable heat pack or warm water poured from a watering can. Do not use boiling water straight from the kettle as this could damage the pipe" (Baxi). Then reset. If it freezes every winter, ask the engineer about lagging the pipe or re-routing it inside.
Codes with no safe home fix
Sensor faults (Vaillant F.12, F.13, F.20, F.23), fan faults, flue gas temperature faults (F.25) and a flame detected with the burner off (F.27, which Vaillant calls "a case for an expert") all need the casing opened. Vaillant's own line on these is "don't try to solve it yourself as opening the boiler casing can be dangerous", and in Ireland only a Registered Gas Installer may work on the boiler anyway (CRU).
No code, boiler just off
Check the obvious before the fault list: the timer and thermostat, a tripped switch or fuse, flat batteries in a wireless thermostat, and the pressure gauge. A boiler with a blank display has no power. A boiler with the display lit and no code is usually waiting for a call for heat that isn't coming.
What to tell the engineer
- The make and model, from the sticker on the boiler
- The exact code, and whether it comes back after a reset
- What the pressure gauge reads cold
- Whether other gas appliances work
- What the weather was doing when it started
- When it was last serviced
Dublin engineers who publish a call-out or repair price charge €80 to €160, middle figure €115, with parts extra (22 October 2026). A code that points to a part is quicker and cheaper to fix than "it's just stopped". See boiler repair in Dublin.
Questions people ask
What does F22 mean on a Vaillant boiler?
Low water pressure in the system, below the normal 1 to 1.5 bar, or a fault with the pressure sensor, its wiring or the expansion vessel. Top up to 1 to 1.5 bar. If the gauge is already above 1 bar, Vaillant says it's a case for an engineer.
What does F75 mean?
On a Vaillant boiler, the pressure change is too low when the pump starts: low pressure, air in the system, a faulty pressure sensor or a failed pump. Top up first; if it recurs, call an engineer.
What does L2 mean on an Ideal boiler?
Ignition lockout. Ideal says to check the condensate pipe for blockages first, then whether other gas appliances work, then the gas meter and any prepayment credit. Then contact Ideal under warranty or an engineer.
What does E133 mean on a Baxi boiler?
The boiler has shut down, and Baxi says the condensate pipe may be frozen. Thaw it with warm water or a hot water bottle, never boiling water, then reset. The same advice covers E28, E53, E119 and E128.
What does F28 mean on a Vaillant boiler?
No flame was detected during ignition. Vaillant lists too little gas reaching the boiler, a blocked condensate pipe, the ignition electrode, the PCB and the flue. Check other gas appliances, prepayment credit and frozen pipes first.
Can I reset my boiler after a fault code?
Once. Vaillant and Ideal both say a reset can clear a fault or get the boiler going temporarily. If it locks out again, stop resetting it and book a repair.
Sources (3)
Prices and facts on this page were checked against these published pages. We are not connected to these businesses.
- Vaillant boiler fault codes: vaillant.co.uk
- Ideal Heating, Logic System troubleshooting: idealheating.com
- Baxi, error codes E23, E53, E133, E119 and E128: baxi.co.uk
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