I have a Vaillant Sine 18. It was in the flat we bought - I've never
looked at it just checked it had no Co emissions, but now it seems to
have developped a problem.
Essentially it works fine while heating but it would not kick in when it
should be at opening the hot water tabs. It started doing it with the
shower. Since we are on the top floor I thought there'd be a problem
with water pressure, but now it fails to kick in with any hot water
tabs. If I switch on the main heating while the hot water tab is open it
would also heat the water.
My knowledge of boiler is limited but I did a search and found a similar
Could it be an expasion vassel problem?
When the boiler is cold the pressure reads about 1bar, and it goes up to
2.2bars when switching on the heating.
If so is it hard to fix it? Have I got to call an engineer or can I do
Many thanks in advance
PS: Quoting original message found on google:
Subject: Re: Boiler - Fix or replace ?
I work for BG,I suggest you get someone who knows about combi's to
have a look at your valliant sine18. By what you are saying there
doesn't seem much wrong with your boiler.There are a few checks to be
made before a fault can be pinned down,don't let a guy guess the
fault,it will cost you money and eventually he will find the faulty
conponant after half the boiler is changed.
If the expansion vessel has lost its charge,it will need to be pumped
up to 0.7-0.9 bar.the easy way to check this without the use of a
pressure guage is to check the pressure on the front of your boiler
is at 1bar cold,then turn on your heating,if the pressure rises up
past 2bar then the expansion vessel needs repressurising.
The fault with no hot water usually lies with the changeover valve's
wax capsual or valve not making the microswitches.