Vailant ecotec plus 824 f75

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Kewat66

Kewat66

Gas Engineer
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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
 
Kewat66 said:
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
Click to expand...

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

It thinks there is no water in the system.
 
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.
 
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.
 
Expansion vessel with no charge, especially on larger systems, can throw up all sorts of problems, including F.75
 
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.
 
Could be too much inhibitor in the system. It froths up in the pump and does not allow the sensor to read the pressure drop when the pump kicks in.
 
There's a thermal fuse on the top of the boiler. If you follow the wire down to the plug hanging on the RHS link it out. If it lights then the thermal fuse has popped. You cannot get them from vaillant...it's a new heat exchanger (not such a good boiler now are they??). Had a lot of to - ing and fro - ing when with BG regarding vaillant. Vaillant say it cannot guarantee safety (alarm bells call 'elf n safety)if this pops. it's a con.
 
if the thermal link has popped its a different fault code my bet is on crud behind the sensor drain it remove sensor then start to fill see if it clear youll need a towel
i can never understand why vailants dont have a screw in the well to allow you to drain the water that collects there when changing parts
 
It can only be the pressure sensor, buy a spare and plug it in dry. Fire the boiler by pushing it in manually. If it runs ok it's some sort of blockage not pump.
 
I have removed the pump head and cleaned, removed the new pressure sensor, removed the sensor housing and cleaned the filter. I tried all the suggestions so far and kept getting the same issue so as a last resort put back the old diverter valve and no fault just the original fault of diverter valve not giving any dhw so I am now assuming the new diverter valve has an issue on it. It seems to be a new modified part with a different electrical connection so of to the shop in the morning to exchange. Fingers crossed!
 
Kewat66 said:
I have removed the pump head and cleaned, removed the new pressure sensor, removed the sensor housing and cleaned the filter. I tried all the suggestions so far and kept getting the same issue so as a last resort put back the old diverter valve and no fault just the original fault of diverter valve not giving any dhw so I am now assuming the new diverter valve has an issue on it. It seems to be a new modified part with a different electrical connection so of to the shop in the morning to exchange. Fingers crossed!
Click to expand...

You've spent some time in front of that boiler mate?
 
Is that not the vailants with the stupid black hose that clogs going into heat exchanger, I've changed a few of them on the 837 models,
 
If you've had the pump head off... was there a whiteish residue? If so open a drain off and the filling loop and flush some fresh water through. A trick from a friend who is a Vaillant engineer.
 
The vain if my life , had 5 in the last two week horrible horrible horrible
 
I've had this one before, spent ages working it out.
The pump had slowed down, I know you said you checked this but was the pump strong.
i weak pump can give this fault.
 
Ps, when you take the old sensor out jab something in the pipe itself to make sure that aint blocked.X
 
How do you check for a weak pump on these? When you take the centre screw out, it pee,s out a jet of water. Usually in the direction of the pcb!
 
With loads of towels,
measure the peeing out! Lol
take the pump screw out and see if it shots out have one hand on the control to switch off
 
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