http://www.omegaowners.com/forum/YaBB.pl?num=1196616207Hi Mickmv6, and welcome. A few folk on here have
had a similar problem and found that the info on the
above link by bates1963 useful in fixing the problem.
If there's plenty of hot coolant in the matrix then I
doubt that the HBV is your problem, but as you have
an MV6 and probably climate control then I don't
know the Vac system layout to be certain. Someone
else on here with the same system will put you
straight.
Best of luck.

It can't be much fun with no heat in
this weather.