If your ATAG boiler has shut down or is displaying an error code, it’s not a sign that the system has failed. It’s actually designed to do it. Modern ATAG boilers are equipped with safety systems that automatically place the boiler into lockout mode when a fault is detected. This prevents damage and ensures the heating system operates safely.
So, why would your ATAG boiler engage lockout mode?
Why Do ATAG Boilers Go Into Lockout?
Lockout is a protective measure. It usually happens for one of a few reasons:
- The boiler pressure is too low,
- There is an ignition failure due to a lack of gas supply.
- Circulation is poor, and the appliance begins to overheat,
- Or the power supply has been interrupted.
When this happens, the boiler stops running and displays a fault or error code on the screen. These codes indicate the cause of the shutdown and are useful for diagnosing the issue yourself or for passing on to an engineer. It’s always worth writing the code down or taking a photo of the display before touching anything.
Here is a list of standard error codes:
| Error Code | Description |
|---|---|
| 10 | Outside sensor error. The outdoor temperature sensor is missing, malfunctioning, or out of range. |
| 20 | Flow sensor error. The sensor that measures flow temperature is out of specification or has a wiring issue. |
| 40 | Return sensor error. The temperature of the fluid returning to the boiler is not being detected properly. |
| 78 | Water pressure out of range. This means the system pressure is either too high or too low. |
| 101 | Overheat error. This happens when the boiler has detected a temperature above the safe limit. |
| 108 | Pressure needs filling (system pressure too low). This is a common issue that most homeowners can sort out. |
| 109 | Pressure > Pmax error (system pressure too high). This indicates excess water pressure. |
| 129 | The fan doesn’t start, and the boiler fan has failed to initiate properly. |
| 133 | No flame after five ignition attempts. Ignition or gas supply issue. |
| 151 | Fan error or control unit defective. Speed control not achieved or defective board. |
| 201 | The Domestic Hot Water (DHW) probe is damaged. Problem with the hot water temperature sensor. |
| 203 | Tank probe damaged. Issue with the tank’s temperature sensor. |
Depending on the code, you should conduct some basic checks before resetting it.
Checks to Make Before Resetting an ATAG Boiler
Before pressing any reset button, take a moment to check the basics. It can save time and sometimes solve the issue altogether.
Start with the gas supply. If the boiler is displaying an ignition-related error, first verify that gas is reaching your home. The simplest way is to try lighting another gas appliance, such as a hob. If that doesn’t work either, the problem lies with the gas supply, and not the boiler. Resetting it won’t resolve the issue, but please contact your gas supplier.
Next, check the boiler pressure. ATAG boilers operate best when the pressure gauge reads between 1.0 and 1.5 bar when cold. If the needle is below this range, top it up using the filling loop until it is back within limits. If the pressure is too high, bleeding a radiator can safely reduce it.
Finally, check that the boiler has power. ATAG boilers are usually wired into a fused spur located near the boiler. Make sure it is switched on. If it already is, check your household fuse box to see if a breaker has tripped. Reset it if needed.
Only once gas, pressure, and power have been confirmed should a reset be attempted.
How to Reset an ATAG Boiler
The exact reset method varies by model, but most ATAG boilers follow a similar principle. Some models have a physical reset button on the control panel. Press and hold this for a few seconds until the display changes or the boiler attempts to restart. On other models, the reset function is found through the digital control menu.
Use the display buttons to navigate to “Reset”, select it, and allow the boiler to run through its restart process.
The boiler will then perform its internal safety checks and, if the original issue has been resolved, it should ignite and return to regular operation.
If it doesn’t restart or immediately shuts down again, avoid pressing the reset button repeatedly.
When Resetting Is Appropriate. And When It Isn’t
It is fine to reset an ATAG boiler when the fault appears minor and you’ve fixed the likely cause, for instance, topping up low pressure after bleeding radiators, or following a momentary power cut. If it is the first time the error has appeared and nothing sounds or feels unusual, a reset is a reasonable option.
However, you should not reset the boiler if the same error keeps occurring, if the boiler makes banging or whistling noises when trying to fire, if it overheats or cuts out again immediately after restarting, or if you are simply unsure what the fault code means. Repeated resets won’t fix an underlying issue and, in some cases, can exacerbate it.
When to Call a Professional
If, after a reset, the boiler still refuses to operate normally or keeps entering lockout, it’s time to stop and contact a Gas Safe registered engineer. Provide them with the error code you noted earlier, along with the model of your ATAG boiler and anything you’ve already checked. This helps them diagnose the problem quickly and carry out the correct repair.
WarmZilla can connect you with trusted local engineers who specialise in ATAG boilers. They can often get someone out within 48 hours, meaning you’re not left in the cold.
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