Vaillant ecotec pro 28 showing f75 but not sensor.

[itchytriggafinga]

hello everyone, have a problem i hope someone can help with.
I have a vaillant ecotec pro 28 showing fault code f75. have taken out the water pressure sensor and got a bit of dirt from it and then changed it from the old pink one to a black one. I have cleaned the filter behind the water pressure sensor and checked the pump for resistance which was 230 ohms. Im getting 240v from the timer to the pcb but when i reset the boiler with my meter across live and neutral on the pump i wasnt getting any voltage before it locked out on f75- which takes about 20 seconds.
So i changed the pcb on the advice of a 'vaillant tech'. Still getting f75 so i tried the wiring lumes still getting f75.
Please help.
Simon b

 

[Andygasman2010]

Did you definatly 100% for sure have no power to the pump at any point before F75? This is important as there is a known fault to do with F75. It sounds like you may not have done the check right seeing as a PCB hasn't cured it.

The PCB knows it's asked the pump to come on and seen that it hasn't, and so logged F75. So PCB/wiring loom would be the only cures for that.

Assuming the pump was on, there is actually a known fault to do with F75. Vaillant stupidly use the pressure switch to detect pump flow by seeing the slight negative pressure it produces when it comes on. If you have a particulary big system you don't always get enough negative pressure. More likely, the expansion vessel needs recharging to about 1bar.

Did you say you'd changed the sensor??

 

[gas4you]

Strange, the board looks for a 0.2 Bar pressure increase to prove the pump is working

 

[itchytriggafinga]

Did you definatly 100% for sure have no power to the pump at any point before F75? This is important as there is a known fault to do with F75. It sounds like you may not have done the check right seeing as a PCB hasn't cured it.

The PCB knows it's asked the pump to come on and seen that it hasn't, and so logged F75. So PCB/wiring loom would be the only cures for that.

Assuming the pump was on, there is actually a known fault to do with F75. Vaillant stupidly use the pressure switch to detect pump flow by seeing the slight negative pressure it produces when it comes on. If you have a particulary big system you don't always get enough negative pressure. More likely, the expansion vessel needs recharging to about 1bar.

Did you say you'd changed the sensor??

Thanks for the speedy reply Andy.
yes i changed the sensor first thing after reading on here the pink ones were faulty. When i tested the pump i removed the green plug in pump connector and put my meter across live and neutral prongs then switched on the boiler reset it and never got a reading. was that the right way to test it?

 

[Andygasman2010]

Yea that should work. Personally i'd leave everything on the boiler pugged in and intact and check the voltage to the pump at two exposed terminals, maybe where it connects to the PCB, or at the pump itself.

Double check this, i'd put money on it being that known fault i've described earlier!

recharging the expansionvessel sounds like an odd solution but it will work if it's what i suspect. If all else fails vaillant have a modification that can be done

 

[itchytriggafinga]

Yea that should work. Personally i'd leave everything on the boiler pugged in and intact and check the voltage to the pump at two exposed terminals, maybe where it connects to the PCB, or at the pump itself.

Double check this, i'd put money on it being that known fault i've described earlier!

recharging the expansionvessel sounds like an odd solution but it will work if it's what i suspect. If all else fails vaillant have a modification that can be done

i did try it with everything plugged in first but when there was no voltage tried it the other way. if i double check that tomorrow and still no voltage recharging the expansion vessel may fix it?

 

[Andygasman2010]

Hmm it's VERY strange to have changed a sensor, a wiring loom and PCB and still have no power to the pump. What I would do is :- Turn off the boiler at the mains, set-up the multimeter accross the live/neutral pump wires at the PCB (or pump itself) turn back on the mains and put a demand on the boiler. See if you pick up any voltage before F75. Sorry if I sound slightly patronising there but it's a strange fault your describing unless there was actually power to the pump, in which case it can be explained fairly easily.

Might be worth checking your multimeter on a known source first, try it on the incoming mains to the boiler, obviously that should be 240Vac.

Double check all this first because if you don't actually have power to the pump at all, I can't help you! You'll probably have to get Vaillant out. How old is it?

 

[itchytriggafinga]

Hmm it's VERY strange to have changed a sensor, a wiring loom and PCB and still have no power to the pump. What I would do is :- Turn off the boiler at the mains, set-up the multimeter accross the live/neutral pump wires at the PCB (or pump itself) turn back on the mains and put a demand on the boiler. See if you pick up any voltage before F75. Sorry if I sound slightly patronising there but it's a strange fault your describing unless there was actually power to the pump, in which case it can be explained fairly easily.

Might be worth checking your multimeter on a known source first, try it on the incoming mains to the boiler, obviously that should be 240Vac.

Double check all this first because if you don't actually have power to the pump at all, I can't help you! You'll probably have to get Vaillant out. How old is it?

Im not sure how old it is,i will double check for voltage today but was getting 240v on the incoming main. How long are the vaillant warranty on a new boiler is it one or two years? And can I just show a receipt for the warranty.

 

[Andygasman2010]

I thought it was three or even five years! Phone them up, you'll need the serial number.

 

[itchytriggafinga]

I thought it was three or even five years! Phone them up, you'll need the serial number.

I phoned them this morning and managed to get it registered as it hasn't been registered before and they are coming out to fix it free. Cant believe it!!!!

 

[Andygasman2010]

Great news! Post back when it's sorted, i'm interested to know. Thanks.