Has my boiler's pressure sensor broken?

[Ali81]

Hi,

Quick question, as I can't really find the answer on Google or this forum.

My Glow Worm Flexicom 18sx comes up with the F9 pressure sensor fault when firing up unless the pressure when cool is 2.0 bar. It used to be fine starting up from 1.6 bar, but the fault kept coming back and increasing the pressure 'fixed it' each time. Now when hot it gets above 2.5 bar, so I took some water out and dropped the pressure to 1.9 bar when cold. Same problem. I've had to top it up to 2.0 bar and now it's working.

So I'm guessing a pressure sensor fault? It also sometimes sounds like there air noises in the boiler when trying to start - is that something that can happen?

 

[ianmcd]

They are very unreliable, and prone to constant failure if the system water is dirty

 

[old duffer]

if an analogue gauge was not working due to a blocked bourdon tube then you would have no readings at all.
If its a digital sensor then they use strain gauge sensors which operate on resistance over a wire.

Please explain how "dirty water" comes into play here

 

[Ali81]

It's a digital display, but I don't know what type of sensor. Water from 3 radiators was clear. I didn't bleed the other 4.

 

[picasso]

Glow worm pressure sensors have a “hole” in the part that sits in the system water, dirt can block the hole and give wrong readings.

 

[old duffer]

but if the "hole" is blocked then how can it work at all?

 

[picasso]

It can trap water inside giving a false pressure reading, before you start with “that’s not the op’s problem “ you asked how dirty system water comes into play.

 

[old duffer]

It's a digital display, but I don't know what type of sensor. Water from 3 radiators was clear. I didn't bleed the other 4.

In which case I can't understand how "dirty water" effects conduction of a current along a wire. So either the sensor is out of range and needs replacing or its giving you accurate readings.
You can always test the pressure in the circuit easy enough but you need to compare the cost of the simple gauge vs a new sensor.
The pressure is very high @ 2.5bar and keep increasing the pressure is not a good idea
As the resistance data is being used elsewhere in the circuit then I'd go with replacement option

 

[Madrab]

Doesn't need to be totally blocked for it to give false/mis readings. OP needs to get someone in to get it checked, cleaned or replaced as required. They're not expensive so it's usually a replacement.

 

[ianmcd]

if an analogue gauge was not working due to a blocked bourdon tube then you would have no readings at all.
If its a digital sensor then they use strain gauge sensors which operate on resistance over a wire.

Please explain how "dirty water" comes into play here

you need to do more googling, you are miles out

 

[CBW]

https://boilerboffin.com/6-causes-of-vaillant-f75-and-glowworm-f9-fault-codes/

I am in no way condoning working on your boilers, just merely for educational and helpfulness purposes.

 

[Razor900]

but if the "hole" is blocked then how can it work at all?

Because it's a pressure transducer.

If the hole gets blocked whilst there's pressure the sensor it'll read the same thing forever...