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.

Vaillant ecotec plus 824 problems

I have vaillant boiler problems and would like some help on troubleshooting the issue.  I have a vaillant ecotec plus 824 and randomly the boiler does not ignite the burner.  I get the fault s.33 where the vaillant boiler manual tells me it is a problem with the air/flue system.  I have had a service guy check the boiler twice and the problem always comes back.  Any help would be greatly appreciated


Ricky M


The problem with your boiler is the air pressure switch located on the top of your boiler.  Check out the parts diagram here.

This part has a diaphragm that has become blocked.  During normal operation when the fan activated air is sucked through the flue and a small amount fills the diaphragm and makes the electrical contacts within the switch.  In your case the flue is blocked and air is not inflating the diaphragm, your diaphragm has a hole, or your contacts are perished.  I would advise you get a corgi man to replace this part to ensure ongoing reliability of your boiler.