Vaillant ecoTEC plus 831 low/high pressure problem

[mamalovesmambo]

Hi,

I have a Vaillant ecoTEC plus 831 boiler.
A few days ago it had a F22 error code displayed, which means low pressure.
I filled up with water, but by the next morning the pressure was low again.
There are no radiator leaks that I can find.

I filled with water, to the appropriate level, within the grey band on the pressure guage. I've since noticed that the pressure also went really high. So am thinking that for some reason the pressure goes too high, the boiler jettisons water, and then the pressure drops too low.

What I'd like to know is, what are the possible reasons for this behaviour?
I have an extended warrenty with Vaillant, and have booked a call-out for them to come and fix the boiler. But if it turns out not to be a boiler problem, then I'll get charged for the visit! So I want to make sure there's not something else that could be causing the boiler to act this way?

Thanks for your help.

 

[Tibbot]

Problem is covered in FAQ's.

 

[mamalovesmambo]

ooops, thanks!
Seems like it's probably a problem with the pressure vessel,
so we should be covered as it's a boiler problem.
Cheers!

 

[pezperry]

Hello,

I had an ecotec plus 831 installed mid feb 2011, it seemed to run ok for around a month. I noticed one of my radiators had a large cold spot so I turned off heating and waited for boiler to cool sufficiently then bled the radiator, which took out a lot of air.

Since then the boiler seems to be loosing pressure, I have to top up the system with the two valves under the boiler every morning when the boiler has had time to cool over night.

I am getting a bit fed up with having to do this and was wondering what the possible problems could be?

 

[Agile]

The obvious answer is to call the installer!

You have not said what the pressure display does when the boiler warms up the heating!

It sounds as if the integral pressure vessel is not correctly pressurised.

I would always check the air charge pressure but the one day install wonders dont have time to bother to do anything like that.

Call them back!

Tony

 

[pezperry]

I will get in touch with the installer. When the heating comes on, the pressure gauge tends to increase, same with the hot water. When I top up the system using the valves at the bottom (to mid grey section in the pressure guage) it steadily looses pressure over a 24hr period, eventually ending up in the red at the bottom. I have never had a fault code displayed though, so I guess there is still sufficient pressure to prevent the boiler shutting down.

 

[Agile]

When the heating is on the pressure will increase from say 1.5 Bar to about 1.8 Bar and thats quite normal.

If the increase is much more than that it implies the pressure vessel is failed of incorrectly pressurised. Then the boiler protects itself by discharging from the PRV to the vent pipe outside. You can check that is not leaking by placing a bottle over it for 24 hours.

If your boiler seems normal in these respects then there must be a leak. The obvious place would be a rad valve. If you feel all round these and look at your hand for water you may find something leaking.

Depending on what the boiler installer did a leak on your existing system would not be his responsibility.

Tony

 

[pezperry]

Thanks for the advice. The pressure does not increase that much, therefore I guess it would be a leak somewhere. I am fairly sure the outflow pipe that sticks out the exterior wall is not leaking as I have been checking it regularly. I will check the radiator valves tonight. Would it be a case of also getting under the floor and checking the pipes leading up to the rads?

I have also seen this thread:

//www.diynot.com/forums/viewtopic.php?t=160787

The post at the bottom makes me think that the two valves under the boiler are to be left slightly open (or am I talking rubbish?) I think mine have always been in the closed position except obviously when boiler has lost pressure and I need to get the pressure up.

Apologies for all the questions (I am on a steep learning curve with regards DIY).

 

[MANDATE]

No you're not supposed to leave the valves slightly open.
When a filling loop is used to top up the pressure, it's supposed to be removed so there is no chance of water at mains pressure entering the system, other than for filling/topping up.
Sounds to me your expansion vessel has lost some of its 'air' charge, which in turn has allowed the pressure to rise more than it should and has opened the PRV.
From this there would be the need to top up pressure again, but before doing so the expansion vessel needs testing/recharging.
You may find that solving the problem of the expansion vessel does not cure your problem fully, because once the PRV has been opened it seldom re seats properly. Silt may be on the valve seating face which allows a small leak, so even when cold the pressure may drop overnight.
Of course with heating on and an increase in pressure the rate of leakage will be more.
You will find many cases where the PRV has had to be replaced because of this problem, but dont replace it until the expansion vessel has been sorted or you'll be back to square one

 

[pezperry]

Hmmm sounds expensive, slightly frustrating that I am having this problem so soon after having the new boiler installed. Oh well, I will post the results up soon.

Thanks everyone for your help.

 

[Agile]

The post at the bottom was a test which you can do overnight by closing the two heating isolating valves completely and seeing if the pressure goes down overnight on the boiler.

If so its a leak in the boiler.

If not and the pressure goes down when its opened in the morning then its a leak in the system as you probably have.

Tony Glazier