Valiant Ecotec plus 831 pressure issue

[chieflasagnaeater]

Hi,

My boilers symptom is it's normal operating pressure, to ignite, is about 2 bar which is middle of the grey on the gauge. Once fired it increases to some 2.8 bar. (The Valiant eng has set CH temp to high as I have a Rf thermostat.)
Have just drained the system and repressurised the EV to 1 bar but this has not helped. Is there anything obvious to check before getting an engineer in.
PS. Had it serviced in August. In Sep drained and refilled to fit a new kitchen rad and it seems since then it has not been right.

Thanks,
CLE

 

[The831Bunny]

The cold fill system pressure should only be 1.0 - 1.5 Bar maximum. If you have a large volume system (approx 12+ radiators or above) you may need to add an additional expansion vessel to the system.

All things equal a sealed system should rise a maximum of 0.5 Bar from cold to operating temperature. Less is preferable. If this is the case on your system and the expansion vessel is charged correctly, you need an additional vessel.

Also a reminder that removing the front casing of the boiler, even to check the vessel, is beyond the gas safety regulations scope of a DIYer I'm afraid.

 

[ALCPlumbing]

Unless the pressure is going through the roof and dispersing water through the PRV then I wouldn't really consider it a problem. As stated you possibly need a larger vessel so may have to add an additional one external to the boiler but if it's all working why are you even worried?

 

[chieflasagnaeater]

You make a good point about the system cold fill pressure ideally 1-1.5bar because at that level my gauge is only just off zero....presume the gauge could be faulty!

I have 4 rads and 2 hydronic plinth heaters downstairs and 4 rads upstairs so would think the internal expansion vessel is sufficient.

ALCPlumbing, to expand on the problem I have, I get F75 fault if the cold pressure is below 2.0 bar and then when heating is on full whack it often auto cuts out if the pressure goes above 3 bar.

 

[Terry lambert]

theyre are a few things that can cause F75. Any competent engineer should be able to fix this.

It's at the crux of your problem

 

[Tipper]

If you check the pressure as read by the pcb by pressing the bottom left button on the control panel you can see just how useless the pressure gauge is.

 

[The831Bunny]

If you check the pressure as read by the pcb by pressing the bottom left button on the control panel you can see just how useless the pressure gauge is.

...or the pressure sensor

 

[Bunnyman]

The gauge is more likely right with the symptoms u describe

 

[chieflasagnaeater]

I have had the pressure sensor replaced. The digital readings are now lower and look more realistic....low grey reads approx 1 bar.
However, the pressure still increases from 1 to about 2.6 bar with CH and DHW demand.

 

[Dan Robinson]

Expansion vessel needs checking /charging

 

[chieflasagnaeater]

Thanks Dan, will give that a go this weekend.

With the system drained, EV pressure should be at 3/4 to 1 bar right?

 

[chieflasagnaeater]

The EV was at 1.6bar. Repressurised to 0.7 and all now seems fine.

...thanks!