Dettson
Overpressure During Operation
Boiler pressure rises excessively during heating and relief valve opens
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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
Failed expansion tank, Fill valve overfeeding, Blocked expansion tank connection, Overheated Dettson boiler due to flow restriction
How to Fix / Troubleshooting
Safety: High pressure can cause scalding and equipment damage. Do not cap the relief valve discharge.
- Check cold pressure: When the system is cold, note the pressure. If it is already high (>20 psi), the fill valve may be overfeeding.
- Test expansion tank: With the system depressurized, measure the air charge in the expansion tank (technician task). Recharge or replace if the bladder has failed.
- Inspect isolation valves: Ensure any valves between the boiler and expansion tank are open.
- Service fill valve: A stuck fill valve should be repaired or replaced by a professional.
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Repair Difficulty
Hard
4/5
Required Part
Hydronic expansion tank
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