Discharge gas sensor failure
The PP2 error code on Grant boilers indicates discharge gas sensor failure.
Grant PP2 means: discharge gas sensor failure. On this component the documented failure modes are the gas sensor has failed — short circuit or open circuit or wiring, connector or harness of the gas sensor damaged or loose. A Gas Safe registered engineer should diagnose the root cause.
What Does PP2 Mean
The PP2 code is shown by the boiler’s control board when it detects discharge gas sensor failure. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows PP2 and the boiler stops until the fault is cleared |
Common Causes
The manufacturer does not publish a cause list for this specific code. The causes below are the failure modes documented for the same component on other boilers, confirmed by the service literature of 8 different manufacturers.
| Cause |
|---|
| The gas sensor has failed — short circuit or open circuit |
| Wiring, connector or harness of the gas sensor damaged or loose |
Safety Warning
PP2 is a gas-related fault. Never attempt to repair or adjust the gas valve, burner assembly, or flue system yourself. All gas work must be carried out by a Gas Safe registered engineer (UK) or licensed HVAC technician (US). Repeated resets after ignition failure can cause unburnt gas to accumulate inside the combustion chamber — this is a serious safety hazard. If you smell gas at any point, turn off the gas supply at the meter, open windows, leave the property, and call your gas emergency service immediately. Gas-related fault. Do not open the boiler casing or attempt repairs to the gas valve, burner, ignition or flue. Repeated resets are unsafe. Diagnosis and repair must be carried out by a Gas Safe registered engineer.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
Step-by-Step Diagnosis
1. Identify which sensor is faulty from the error code (flow, return, DHW, flue gas, or outdoor). 2. Check the wiring — inspect the connections at both the sensor and the PCB for corrosion or loose terminals. 3. Measure the sensor resistance with a multimeter — compare with the manufacturer's resistance/temperature chart (typically 10kΩ at 25°C (77 °F) for NTC sensors). 4. If resistance is out of range (infinite = open circuit, near zero = short circuit), replace the sensor. 5. If resistance is correct, check the wiring continuity between the sensor and PCB. 6. If wiring is good, test the PCB input
How to Fix It
Measure the resistance of the gas sensor with a multimeter and compare it against the manufacturer’s resistance-versus-temperature table; replace it if it is open circuit, short circuit or out of range.
Unplug and re-seat the connector of the gas sensor, then check the harness for chafing, corroded pins and breaks in continuity.
Refer to the Grant service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Grant models that can display fault code PP2:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Grant models | — | Possible |
Frequently Asked Questions
Measure the resistance of the gas sensor with a multimeter and compare it against the manufacturer’s resistance-versus-temperature table; replace it if it is open circuit, short circuit or out of range. According to the technical documentation, this is the first check on the list for PP2.
PP2 is classified as a high-severity fault: it involves gas, combustion or flue components. Do not keep resetting the boiler and do not attempt the repair yourself — call a Gas Safe registered engineer.