Boiler help

[RTX 3090]

Hi, I have a Vaillant EcoTech Pro 28 and it is giving me an F75 error. Normally I would just slightly pressurise it and it will work again after firing it. Now it only works when I pressurise it really really high, like 3.3 bar. Even then I have to pressurise the system every few hours. If I depressurise the system to around 2.5 bar, it will not fire and keeps returning F75. The pump is fine as I can hear it humming. I am convinced the temperature sensor is fine as the digital display reads the pressure fine, but the boiler only fires under high pressure. 

[tikker]

Probably best to call an engineering company (or whatever the right term for boiler companies is), perhaps the one that installed it, and get them to check it out. If you still have the manual, it most likely also will list what the code means.

 

https://householdquotes.co.uk/vaillant-fault-code-f75/

If this is accurate it seems it's either a broken pump or a faulty pressure sensor somewhere.

 

19 minutes ago, RTX 3090 said:

If I depressurise the system to around 2.5 bar, it will not fire

19 minutes ago, RTX 3090 said:

it only works when I pressurise it really really high, like 3.3 bar

That does sound like a pressure sensor issue to me, or at least something related to the pressure. In any case, I would get an egineer (which I'm not) to check it out for a professional answer

[RTX 3090]

1 minute ago, tikker said:

That does sound like a pressure sensor issue to me, or at least something related to the pressure. In any case, I would get an egineer (which I'm not) to check it out for a professional answer

Does a gas safe guy have to come and change the sensor or can I order one of eBay and do it my self. 

 

2 minutes ago, tikker said:

Probably best to call an engineering company (or whatever the right term for boiler companies is), perhaps the one that installed it, and get them to check it out.

All the good ones are either closed or really busy and can't come, there are a few sketchy ones but I want to avoid them as we followed their advice and ended up breaking the diverter valve. I also don't want to pay £100 for a £10 part

[RTX 3090]

17 minutes ago, tikker said:

If you still have the manual, it most likely also will list what the code means.

It says low pressure but the system only fires when I set it way too high. I did 3.3 bar

[tikker]

2 hours ago, RTX 3090 said:

It says low pressure but the system only fires when I set it way too high. I did 3.3 bar

Does the manual say what pressure range it should be in? What do you mean by "when I set the pressure"? You mean adding water right? It could also be trapped air that needs to be let out.

2 hours ago, RTX 3090 said:

Does a gas safe guy have to come and change the sensor or can I order one of eBay and do it my self.

It's water pressure, not gas. Gas is just used to heat the water. You need water pressure to pump it around your house. In any case these kind of units are not user servicable and it would definitely void any warranty you may still have. Not to mention you may do more harm than good if you don't know how to do it properly. Before you do anything you need to know what the problem is anyway. Right now you know it's something with pressure, but you still don't know what. A technician is probably the only one that can tell you.

 

The manual of that  thing says this:

https://www.vaillant.co.uk/downloads/product-manuals/ecotec-pro-1/ecotec-pro-24-28-combi-installation-and-maintenance-instructions-1943267.pdf

Message:

F.75 Fault: Pump/ water short-age

Possible cause(s):

Insufficient pressure jump detected when starting the pump

Measure:

1.  Check: Water pressure sensor, heating pump (blockage),heating circuit (air, sufficient water volume), adjustable by-pass, external expansion vessel (must be connected at the return). Activate check programme P.0.

2.  If a low loss header or heating pipes with a diameter greaterthan 1 1/2 inch are installed, replace the 3/4-inch seal in theheating flow with a screen. If required, install the F.75 serviceset.

[RTX 3090]

8 minutes ago, tikker said:

You mean adding water right?

Yes

8 minutes ago, tikker said:

It could also be trapped air that needs to be let out.

I drained 5L out of the system and pumped more in, and bled all radiators, so I don't think it is trapped air

10 minutes ago, tikker said:

id any warranty you may still have.

none, unfortunately.

 

22 minutes ago, tikker said:

It's water pressure, not gas.

But would I get arrested as apparently it is an criminal offence to repair a boiler yourself

 

36 minutes ago, tikker said:

Right now you know it's something with pressure, but you still don't know what

I get an F75, so I pressurise it higher then what I should. It then works (like the full house heating comes on) but tells me the pressure is way to high. So I depressurise then it doesn't work again. If the sensor is not working it would not start even at higher pressures. If the sensor is out of calibration, how does it know what the real pressure is (it tells me pressure is too high, how does it know that if it is out of calibration). So I'm confused at this point, should I drain the entire loop and refill it

[tikker]

1 hour ago, RTX 3090 said:

But would I get arrested as apparently it is an criminal offence to repair a boiler yourself

Depends on the country you are in I guess, but it's certainly not the most safe thing to service without proper education in servicing them. You are dealing with gas, water and electricity combined in addition to pressurized vessels so it can be plain dangerous to mess around with. @Keith Wmay have your answer to that.

 

1 hour ago, RTX 3090 said:

I get an F75, so I pressurise it higher then what I should. It then works (like the full house heating comes on) but tells me the pressure is way to high. So I depressurise then it doesn't work again. If the sensor is not working it would not start even at higher pressures. If the sensor is out of calibration, how does it know what the real pressure is (it tells me pressure is too high, how does it know that if it is out of calibration). So I'm confused at this point, should I drain the entire loop and refill it

So according to the manual (I edited the post) it is related to the pump and/or pressure. It could be a malfunctioning sensor giving you erratic behaviour, something else could be broken that only still responds at the highest pressure, it could be that you activate some sort of protection mechanism at such high pressure to prevent it from damaging itself or creating a dangerous situation, or it could be a faulty sensor with the high 3.3  bar actually being normal 2.5 bar and the list goes on.

 

Draining and refilling probably won't have a meaningful effect. In any case you would only put yourself in danger and risk damage to the house or equipment if you attempt to do anything yourself, because you don't know what you are doing and don't know what the problem is.

 

In short: no you cannot service this yourself and need to get a technician to look at it.

[WkdPaul]

* thread locked *

 

Please call a professional, it's not worth the potential issues (legal and/or health) to try and save a few pounds.