Vaillant ecoTEC plus 837 R1 with persisting F75 fault

[yossibac]

Can someone help diagnose Vaillant ecoTEC plus 837 with persisting F75 fault please?
We already replaced the pressure sensor, installed F75 kit, replaced the main heat exchanger, and the pump, and the PCB, and flushed the system and installed a filter on the return, but still sometimes we get F75. The boiler still reset and run, but we would like to get to the bottom of it if at all possible. Thanks in advance.

 

[ShaunCorbs]

Who did the work ?

 

[Noxer]

Blocked flow sensor?

 

[Riley]

Wow that’s some repairs

 

[yossibac]

All those parts has been replaced in the course of 5 years not all at ones, and from different reasons, but the F75 has been creeping out all this time, some times the fault would be gone for months so you think that it was cured. The boiler is otherwise working well. There are two questions: 1) if there is a fault why the boiler always reset and continue to work sometimes for months? 2) if there isn't a fault why is the F75 keep creeping out? Thanks for your thoughts.

 

[Nico]

Do you have to top up the pressure in the system often?

 

[yossibac]

Yes, every three months or so, and it does seem to keep F75 away for a while, we are now on 1.8 bar when cold and 2.1 bar when hot

 

[Nico]

I believe F75 is a fault code for when boiler pressure is too low/ also doesn’t detect an increase in pressure when pump kicks on. Have you ever noticed what pressure your boiler is sitting at when this code is showing?

 

[yossibac]

I noticed that if the F75 starts kicking and if after the first reset F75 returns, it makes it calm down if I top up. Last time boiler was at 1.7 bar before the first F75 kicked in. Generally speaking Vaillant have different fault code for low pressure and the boiler can work very well with 1.2 bar or even a bit lower, but that only if the boiler is not faulty.

 

[Nico]

ah Right could be a number of things. Sound like a defect in the sensor or it’s partially blocked if it needs such a high pressure to pick up anything. Has your expansion vessel ever been investigated as well as everything else you had mentioned?

 

[yossibac]

I will check the vessel. After installing F75 kit is it best to leave the bottom sensor connected or it's best to disconnect it's plug?

 

[ShaunCorbs]

I will check the vessel. After installing F75 kit is it best to leave the bottom sensor connected or it's best to disconnect it's plug?

Best to get a gas safe engy

 

[yossibac]

Best to get a gas safe engy

We are🙂

 

[ShaunCorbs]

We are🙂

So you won't need know the question you asked

 

[yossibac]

So you won't need know the question you asked

I thought that this forum is there to help one another, so sorry for troubling you.

 

[Harvest Fields]

I thought that this forum is there to help one another, so sorry for troubling you.

Smells like DIY to me.

 

[ShaunCorbs]

I thought that this forum is there to help one another, so sorry for troubling you.

You are gas safe or your getting one ?

 

[cmel1975]

has it got an internal condensate pipe ? which could be partially blocked at connection to waste pipe

 

[yossibac]

We have found the solution. For those of you who tried to help, if you would like to know please pm me. And to the others that didn't, no, we are not DIY

 

[Last Plumber]

We have found the solution. For those of you who tried to help, if you would like to know please pm me. And to the others that didn't, no, we are not DIY

Do you have an external pump as well as the one in the Boiler?

 

[Harvest Fields]

I’m good I know what the problem of with that Code. But thanks anyway.

 

[yossibac]

Do you have an external pump as well as the one in the Boiler?

No, there is no external pump

I’m good I know what the problem of with that Code. But thanks anyway.

We all know what F75 is, what we didn't know is why by taking all the appropriate actions it was still there.

 

[Old Account]

We have found the solution. For those of you who tried to help, if you would like to know please pm me. And to the others that didn't, no, we are not DIY

Why would someone as a professional gas safe engineer make the customer poor by changing almost the whole boiler? Why not calling manufacturer and get some information or perhaps get it solved via warranty. It doesn’t seem very good to change all those parts ... very unprofessional

 

[rpm]

Why would someone as a professional gas safe engineer make the customer poor by changing almost the whole boiler? Why not calling manufacturer and get some information or perhaps get it solved via warranty. It doesn’t seem very good to change all those parts . very unprofessional

Apparently changing bits here and there over 5yrs cured it only for it to return after a few months is the answer.