Worcester Bosch A1 229 fault codewhat it means and how to fix it
The boiler has detected a dry-fire condition — it is trying to heat water that is not moving. Turn it off and leave it off until an engineer has seen it.
Stop — this needs an engineer
Get a Gas Safe registered engineer to look at your Worcester Bosch A1 229
Gas Safe Register engineers only. No obligation.
When did this start?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
On the first cold day after the heating had been off all summer
A seized pump is very likely. Pump rotors stick after months standing still, and the first call for heat finds them.
An engineer can often free a stuck pump, but if it has seized once it will seize again — budget for replacement.
Straight after plumbing work or a radiator being changed
Air lock. The system was not vented properly after being refilled, and the pump cannot move water against trapped air.
Call whoever did the work back. This is finishing their job, not a new fault.
It has been getting slowly worse over months
A filter or system gradually blocking with magnetite, or a pump losing performance as it wears.
Ask for the filter to be checked and the system water tested at the same visit. Fixing the pump without addressing the sludge just buys time.
What A1 229 means
A1 229 is a pump or circulation protection lockout. The boiler senses that it is producing heat without water flowing to carry it away, which is the condition that cracks heat exchangers. Unlike a low-pressure code, this one can appear with correct system pressure: there is water present, it simply is not moving. The most common causes are a failed or seized pump, a completely blocked filter, or an air lock in the primary circuit. Because the damage from running in this state is both rapid and expensive, this code should be left locked out rather than reset repeatedly to get one more evening of heating.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Pump seized or failed | Common after a long summer standing idle. The pump either does not start or spins without moving water. | Common |
| Air lock in the primary circuit | Frequently follows a drain-down, a repair, or a radiator being replaced. | Common |
| Blocked magnetic filter or strainer | A filter that has never been serviced eventually restricts flow completely. Check the service date on the filter body if there is one. | Occasional |
| Closed isolation or zone valve | Often after other work in the property. Cheap to find, embarrassing to miss. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£280–£700
Time on site
2 hours
Pump replacement £280–£450. Add £400–£700 if the system needs flushing. Freeing an air lock alone is usually within a standard call-out.
Typical UK prices including parts and labour, updated August 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Central heating circulating pump
CH-PUMP-15-60£90–£180Plumbing merchant
Price checked 5 August 2026
Magnetic system filter, 22mm
MAG-22£65–£120Plumbing merchant
Price checked 5 August 2026
What other owners found
Nobody has shared what worked for them on this code yet. If you have had it, you would be the first — and it genuinely helps the next person.
Related Worcester Bosch fault codes
- E9 219Stop — call an engineerThe boiler has overheated and the safety thermostat has tripped. Water is not carrying heat away from the exchanger, and it should not be run until that is fixed.Related: overheat and circulation
- E2 222Get it checkedThe flow temperature sensor is giving a reading the appliance cannot trust. Usually the sensor rather than the temperature.Related: overheat and circulation
- L1Get it checkedThe boiler is not seeing enough water flow through it to run safely, so it has stopped. Usually a pump, an air lock, or a blocked filter.Related: overheat and circulation
- E02Get it checkedThe overheat thermostat has tripped. Almost always this means water is not moving through the appliance properly rather than that it is running too hot.Related: overheat and circulation
- F.20Stop — call an engineerThe overheat thermostat has tripped because the boiler got too hot. It has shut down to protect itself and it should not be restarted repeatedly.Related: overheat and circulation
- A02Get it checkedThe safety limit thermostat has tripped on overheat. In practice this nearly always means water has stopped circulating properly.Related: overheat and circulation
Related guides
Common questions about Worcester Bosch A1 229
The pressure is fine, so why is it saying dry fire?
Because the two are different things. Pressure tells the boiler there is water in the system. This code says water is not moving through the heat exchanger. A perfectly pressurised system with a dead pump produces exactly this fault.
Can I keep resetting it for one more evening of heating?
It is the worst possible economy. You are running a heat exchanger dry to save a call-out fee, and the exchanger costs £600 to £1,200 to replace. On an older boiler that is the end of the appliance.
How much is a new pump?
Usually £280 to £450 fitted, and it is normally done in one visit. If the system is dirty enough to have killed the pump, add a filter and a clean or the new one will follow it.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
- Interviews with working engineers
Checked by Technical reviewer (Gas Safe registration to be displayed on appointment) on 5 August 2026.