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
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
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
The number and the letter on this page do not go together in Worcester's documentation, and it is worth being clear about that before anything else. Worcester's Greenstar i fault table publishes the pump fault as A1 281, described as "pump stuck or running dry", with checks on primary system water pressure, air in the system, circulation within the heating system, and the wiring and operation of the pump.
The number 229 belongs to a different alert code entirely: Worcester give EA 229 as "loss of ionisation signal during operation", which is a flame fault and is covered on its own page here. So if your display shows A1, this page is the right one and the pairing to quote Worcester is A1 281. If it shows 229, you want the flame page. What A1 means 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 September 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 28 September 2026
Magnetic system filter, 22mm
MAG-22£65–£120Plumbing merchant
Price checked 28 September 2026
Own this appliance and had this code? . Nothing is published until a person has read it.
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
- E9 224Stop — call an engineerOne of the two safety thermostats has tripped: the flue overheat thermostat or the high-limit stat on the heat exchanger. Worcester's own check list includes the burner gasket for flue gas leakage.Related: overheat and circulation
- E5 218Get it checkedThe flow temperature sensor has measured water leaving the heat exchanger far hotter than it should be. The boiler shut down to protect itself, and heat is not being carried away fast enough.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
- D1 240Get it checkedThe return temperature sensor has short circuited. The boiler has lost its reading of how warm the water is when it comes back from the radiators.Related: overheat and circulation
- D4 341Get it checkedThe water temperature in the boiler is climbing faster than it should, which means very little of it is moving. Worcester's checks are pressure, air, circulation and the pump, in that order.Related: overheat and circulation
Own a Worcester Bosch boiler? Save it and its codes come first next time.
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.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
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
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.