Vailant ecotec plus 824 f75

[Kewat66]

Hi All,

looking at a vaillant ecotec plus 824. It is coming up with f75. This seems to relate to low pressure and pressure sensor. Have changed the pressure sensor, checked the pump, change the divertor valve ( that was original fault). System pressure is 1.5 and still no joy. Hot water fine. Starts the sequence but fails when it gets to fan and pump running (s05) then fault code F75 appears. Checked the manual and vaillant web site and they say could be a number of related issues!
i am now think PCB board but any ideas before this is bought.

thanks
kewat66

 

[AlexGas]

Hi All,

looking at a vaillant ecotec plus 824. It is coming up with f75. This seems to relate to low pressure and pressure sensor. Have changed the pressure sensor, checked the pump, change the divertor valve ( that was original fault). System pressure is 1.5 and still no joy. Hot water fine. Starts the sequence but fails when it gets to fan and pump running (s05) then fault code F75 appears. Checked the manual and vaillant web site and they say could be a number of related issues!
i am now think PCB board but any ideas before this is bought.

thanks
kewat66

Did you check the filter on the hydro block? Also check that the expansion vessel is charged to the correct level. Hope that the main neat exchanger is not blocked.

 

[Kewat66]

Expansion vessel is charged correctly and filter was clear.

 

[bigads28]

The sensor is faulty, it's not detecting the pump running.

It thinks there is no water in the system.

 

[Ollieg]

Check behind the sensor is clear. Filter. Expansion vessel. The boiler looks for a slight pressure rise as the pump runs. Is the pump ok?
A way to cheat the boiler into firing is close the flow valve and open it when it sparks. If the display temp jumps around its a good sign the pcb is gone.

 

[Ollieg]

Its like I vomited that out.

 

[AlexGas]

Expansion vessel is charged correctly and filter was clear.

Did you drain the boiler down?

 

[Kewat66]

Yes boiler drained down twice

 

[Kewat66]

Pump seems ok as it continues to run when the sequence has stalled. When the overrun is complete the boiler tries to re-ignite and then stalls again.

 

[AlexGas]

Expansion vessel with no charge, especially on larger systems, can throw up all sorts of problems, including F.75

 

[AlexGas]

What colour is the pressure sensor?

 

[Kewat66]

Sensor was black

 

[Ollieg]

Does the temp on the display change when its going through its sequence? like 23 then jumps to 30 when the fan runs for instance. I have had this a couple of times.

 

[Ollieg]

Close the bypass?

 

[Kewat66]

The temperature stays constant