I have a 6month old Vaillant Combi ecoTEC 937.
The pressure keeps rising to 2.8/2.9/3bar.
has anyone got any ideas what could be causing this.
previously when this has happened it has come up with a F81/F91 fault - but in the book there is no reference to F81?? F91 says load storage tank NTC - what does NTC mean??

mark stanley, October 2008

thnaks Iain much appreciated

mark stanley, October 2008

ps, post ch questions in home heating systems otherwise you may be missed. Think most look at plumbing and home heating

iain, October 2008

if the pressure rises only when using your central heating then its an expansion vessel problem.

the expansion vessel is half air half water seperated by a diaphragm. as the system water (radiators) gets hot the water obviously expands and the air section is the part that allows this to happen.

if the expansion vessel is undercharged with air then once expansion starts it'll cope for a little while then pressure will rise when it cant cope no longer.

ive had to recharge a few ecotecs and its solved the problem.

the expansion vessel can generally be flat or dead
flat: press pin in and you'll get nothing out, maybe a little air
dead: press pin in and you'll get water

iain, October 2008