Vaillant Combi Boiler

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F.75 Fault with Vaillant Ecotec Plus 637 Combi Boiler

I need help with my vaillant ecotec plus 637. I am getting a f.75 fault with the system. I have been told this is common vaillant combi boiler problems of this model. So please help.

When it starts its fails to fault f.75, where the vaillant combi boiler manual states no pressure rise was detected on turning on the pump and water pressure sensor and or pump defective.

The pump is fine I have checked it and the unit has plenty of water.

is this a common fault or am I missing something with my basic troubleshooting?


Tim Jones


F75 is a very common fault of this range. If the sensor on the bottom left hand side of the boiler case has an orange cap on it then this is the cause as they are very temperamental. The F.75 fault lights up when the boiler PCB fails to detect a 0.1 – 0.2Bar pressure increase when the pump operates on start-up. Check out the exploded parts lists here.  We also have details of the fault and repair in our troubleshooting page.

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