Vaillant Combi Boiler pressure problem

[sami]

The pressure on my Vaillant combi boiler (Turbomax VUW242E/282E) keeps going down to zero and need to find out why and what needs to be done to keep the boiler producing HW for both the heating and taps. Recently an engineer replaced the valve but that didnt fix the problem.

 

[gas4you]

What valve did he replace? The prv?

Could simply be a leak on your pipe work.

Pressurise boiler, turn off ch isolating valves under boiler and leave as long as possible.

If pressure doesn't drop then it is a leak on the rest of your system somewhere

 

[megawatt]

Could also be the EV and the engineer was a wally

 

[sami]

He replaced the prv as I had the same problem and the overflow pipe was leaking alot. the leaking has stopped and he said that he doesnt think there is a leak, but I should pay him for a power flush which I havent. He also mentioned replacing the EV, but I am not sure if he is just talking rubbish. I hope this makes sense as I am not very good at all of this.

 

[megawatt]

If your EV is faulty (or simply discharged) system pressure will rise past the PRV open pressure (typically 3 bar) and water will be vented from the PRV discharge pipe.

Check the simple stuff first ... EV pressurisation.

 

[sami]

Ok!! so how do I check the EV pressurisation?

 

[megawatt]

Release the system pressure to zero on the guage either from the boiler drain point (ideally) or by releasing through the PRV and check the pressure on the EV schraeder valve with a tyre pressure guage.

If it is below 0.5 bar ...

1. Pump it up with a tyre pump to 0.5 bar.
2. Re-pressurise the system to 1 bar via the filling loop.
3. Turn the system CH on full and watch the pressure guage ... It shouldn't rise above 2.5 bar ('ish).

 

[Agile]

Its actually better to start by discharging all the air from the EV as this will indicate if there is any water on the air said.

I did this with a 25 y.o. Vaillant this evening and it was dry as a bone.

I always recommend air pressure to 0.9 bar and water pressure to 1.5 bar. With heating on it should not rise more than about 0.4 bar.

Tony

 

[Softus]

this will indicate if there is any water on the air said.

Is that the space hovering over Port Said?

 

[megawatt]

Agile Wrote:

I always recommend air pressure to 0.9 bar and water pressure to 1.5 bar. With heating on it should not rise more than about 0.4 bar.

As EV charge pressures relate to system volume ... Any specific reason why Tony?

 

[Agile]

The main reason is that a higher system operating pressure reduces kettling and possibly cavitation on the pump.

It also gives more scope for pressure loss on the gauge to be noticed by the user.

Tony

 

[megawatt]

It gives more scope for pressure loss on the gauge to be noticed by the user.

Don't have a problem with this.

The main reason is that a higher system operating pressure reduces kettling and possibly cavitation on the pump.

I'd need some convincing of this though

 

[Agile]

The main reason is that a higher system operating pressure reduces kettling and possibly cavitation on the pump.

I'd need some convincing of this though

Find a badly kettling boiler and double the pressure!

Or just think of what kettling actually involves, a liquid to vapour transition. Increasing the pressure will lessen the volume of the vapour.

Tony