Discharge gas overheat protection
The PP6 error code on Grant boilers indicates discharge gas overheat protection.
Grant PP6 means: discharge gas overheat protection. On this component the documented failure modes are no water circulation: pump blocked, seized or not running or safety thermostat or overheat limit tripped. A Gas Safe registered engineer should diagnose the root cause.
What Does PP6 Mean
The PP6 code is shown by the boiler’s control board when it detects discharge gas overheat protection. 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 PP6 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 7 different manufacturers.
| Cause |
|---|
| No water circulation: pump blocked, seized or not running |
| Safety thermostat or overheat limit tripped |
Safety Warning
PP6 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. Check the circulation pump — verify it is running and water is flowing (feel the pipes either side of the pump for temperature difference). 2. Check system valves — ensure all isolation valves and zone valves are fully open. 3. Check the system for air locks — bleed radiators and check for gurgling noises. 4. Inspect the heat exchanger — check for limescale build-up or sludge. 5. Test the flow and return thermistors — compare the temperature reading with an external thermometer. 6. Check pump speed setting — increase if necessary. 7. If the system has a filter (magnetic or inline), check if it needs cleaning
How to Fix It
Check the pump is receiving power and turning freely; free a seized shaft or replace the pump if it does not run.
Establish why the boiler overheated — usually no circulation — before resetting. Then check the continuity of the safety thermostat and replace it if it stays open when cold.
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 PP6:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Grant models | — | Possible |
Frequently Asked Questions
Check the pump is receiving power and turning freely; free a seized shaft or replace the pump if it does not run. According to the technical documentation, this is the first check on the list for PP6.
PP6 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.