P1
Junkers
Maximum Flow Temperature Exceeded
Error P1, furnace modulates down or locks out during high demand
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Insufficient system flow, Undersized radiators, Pump failure or incorrect speed, Blocked system filter or valves
How to Fix / Troubleshooting
Safety first: Isolate power before working on hydraulic components.
- 1. Check all valves: Ensure isolation valves under the furnace and on heating circuits are fully open.
- 2. System filter: Clean any installed system filter or strainer to restore flow.
- 3. Pump verification: Confirm that the pump is running and set to an appropriate speed. Replace if noisy, seized, or not circulating.
- 4. System design: If the boiler is oversized for the radiator system, consult a heating engineer about adding emitters or adjusting control settings to reduce cycling and high flow temperatures.
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Repair Difficulty
Medium
3/5
Required Part
Circulation Pump
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