Vaillant eco tec pro 28 F75 fault code.

[Matt0029]

I have a vaillant eco tec pro 28 that is coming up with the fault code f75. The system needs to be pressured to a pressure of 2.3 bar or above to get to work. Obviously when running this is causing an issue with water coming out the pressure relief as it expands up to 3 bar. From my research it looks like it could be the pressure sensor though I think this was swapped recently or the pump. Any one had this fault code were you have had to rise the pressure really high to get the boiler to fire? And diagnosed the problem from this?

 

[Harvest Fields]

How old is the boiler mate? I bet that the system water will be dirty. It doesn’t take much to block them up. Take it out and look down the whole at the bottom. I bet it’s blocked.

 

[Matt0029]

Its about 8 years old, that's why when rising the pressure to 2.3 bar and above it getting the boiler to fire? A blockage is stopping the pressure registering maybe. I did drain the system recently and the water did look quite clear.

 

[kozak1968]

Pressure sensor problem. On older models it was at the bottom where the crud settles. Newer models are higher up (still block up though)

 

[Harvest Fields]

Worth a try as it doesn’t take much to block them up.

 

[Matt0029]

Yeah I looked at that on mine it is right at the back high up. Though think my friends is at the bottom. Are the iso valves on the flow and return usually solid on valliants? So it can be pulled out and a pin pushed through it and check the seating for crude? Also on the older models they are light red. Is it best to swap for a black one?

 

[Harvest Fields]

Yeah I looked at that on mine it is right at the back high up. Though think my friends is at the bottom. Are the iso valves on the flow and return usually solid on valliants? So it can be pulled out and a pin pushed through it and check the seating for crude? Also on the older models they are light red. Is it best to swap for a black one?

Isolation valve are awesome mate. But use an Allen key not grips or adjustables

 

[Last Plumber]

Yeah I looked at that on mine it is right at the back high up. Though think my friends is at the bottom. Are the iso valves on the flow and return usually solid on valliants? So it can be pulled out and a pin pushed through it and check the seating for crude? Also on the older models they are light red. Is it best to swap for a black one?

Allen key is 4mm
You may as well swap it for a new one, they're cheap!

 

[Last Plumber]

Yeah I looked at that on mine it is right at the back high up. Though think my friends is at the bottom. Are the iso valves on the flow and return usually solid on valliants? So it can be pulled out and a pin pushed through it and check the seating for crude? Also on the older models they are light red. Is it best to swap for a black one?

Allen key is 4mm
You may as well swap it for a new one, they're cheap!

 

[Matt0029]

Thanks one further question, is there a filter before the sensor that may need cleaning?

 

[Last Plumber]

Thanks one further question, is there a filter before the sensor that may need cleaning?

Buy a new one. You won't get it out without breaking it I wouldn't have thought so anyway. It's plastic, in behind the sensor on the flow. (bottom left Brass section).

 

[Matt0029]

Thanks so the filter is attached to the sensor, I will buy a new one then.

 

[Last Plumber]

Thanks so the filter is attached to the sensor, I will buy a new one then.

It's in behind it. You take the flow pipe out of that brass section to get it out. If you take the sensor out at the same time you will be able to see it.

 

[Matt0029]

Thanks I am hoping just to swap the sensor. I'll find out tomorrow.

 

[Matt0029]

If taking the flow pipe out to remove the filter does this usually the require a new oring when replacing? Need to get an oring pack for the van.

 

[Last Plumber]

If taking the flow pipe out to remove the filter does this usually the require a new oring when replacing? Need to get an oring pack for the van.

Not normally. A bit of silicone grease is enough more often than not.

 

[Matt0029]

Thanks on removal the filter was clean also the pressure sensor. Though with the new one installed it fires up at 1 to 1.5 bar. Can they just go faulty over time? I mainly work on new builds installing. Am trying to pick up the servicing and repairs side of it.