Water keeps going cold.

[703810995]

Hello.

It's a Vaillant combi boiler and the problem started just as summer ended. The water goes cold (and the heating I think) whenever it chooses, which can be a few minutes or a few days. A simple press of the 'flame'button on the boiler (ecoTEC plus 831) gets the water hot again.

I don't think there is any leaking anywhere underneath. The pressure doesn't seem to be dropping either. It may have gone from around 1.5 to 1.1 but that's over several weeks. I topped it up to 2.0 (not on purpose) and it seems to be maintaining this pressure. When I say I didn't do it deliberately, I meant I turned the valves until it rose to 1.5 and then closed them, but the pressure then slowly climbed up to 2.0 on its own! The water is still going cold.

My main question is that as there are no error messages at all, could a LIKELY culprit be the pressure sensor and what other LIKELY causes could it be?

Thank you.

 

[jj4091]

Do you have a wireless programable room thermostat

 

[CountryFan]

Sounds like a diverter failure. Pressure sensor would likely give a fault code.

 

[703810995]

Thank you for the replies.

Do you have a wireless programable room thermostat

No, it's wired and at the landing at the bottom of the stairs.

Sounds like a diverter failure. Pressure sensor would likely give a fault code.

I never thought I'd actually wish for an error now! So would it be recommended to skip replacement of the pressure sensor as a first step?

Thank you.

 

[CountryFan]

I never thought I'd actually wish for an error now! So would it be recommended to skip replacement of the pressure sensor as a first step?

IME, and I work on them almost daily (Ecotec pro’s - similar to the plus), no, I wouldn’t be looking at the pressure sensor as a 1st step.

 

[Johntheo5]

The status codes S may tell you something, try and access them when the boiler cuts out, someone on here or the attached may tell you how to do it, they do not flag a Alarm.

 

[CountryFan]

The status codes S may tell you something, try and access them when the boiler cuts out, someone on here or the attached may tell you how to do it, they do not flag a Alarm.
View attachment 422316

You press the i button(s)

 

[703810995]

Thank you for the helpful advice.

Good news! Got the 'F.75 Fault Pump water shortage' fault! Never thought I'd be saying that! Assuming it's not the pump or expansion vessel of course!

Sorry for my ignorance but I thought that error messages would be visible after pressing the flame button and the display lighting up. I'm sure this was the case the last time the pressure sensor went. This time, however, there was no error after the display lit up and I am not sure but I don't think I looked at the display before lighting up as it is normally dark and I can't see it without a torch, so I can's say for sure if there was or wasn't any F.75 or any other error displayed on any of the previous times the water went cold.

This time, when the water went cold again, when I went closer to press the 'I' buttons as advised above, I only barely managed to notice that there was an error, the F.75 error.

Pressing the 'i' buttons only gave me the F.75 error, there wasn't any status codes.

So I assume this means pressure sensor replacement as a first step.

 

[Johntheo5]

The fault codes should display without pressing the "I" button but if you press it and the + and - buttons you should get the historical faults.

F.75 is also displayed if the pump pressure doesn't rise on starting the pump, note the boiler pressure when off then start the boiler, the pressure should then rise by say 0.25/0.4bar, (the pump head).

Press (according to AI), the + or - buttons to give a digital display of the pressure and compare this with the boiler gauge pressure, the digital one is what the PCB is monitoring for pressure changes.