Without actually getting as far as firing, my recently installed
Vaillant 418 seems to occasionally do a quick purge cycle - the fan
runs for a few seconds, then stops. The display shows there is no call
for heat. I have noticed it on two mornings. Now why would it do that?
Time clock is set to allow heating only to come on, but the stat is set
to 15C, much lower than the house actually is. HW is set to come on at
16:30 in the afternoon.
My Keston does that every 24 hours of non-use, according to
the manual. In 16 years, I only heard it do it once, but you
need to be in the bathroom at the time, and not having a
shower or anything else noisy, in order to hear it.
I included the same feature in my heating controller for the
mid position valve (which controls upstairs and downstairs
heating zones, not hot water). If it's not operated in last
24 hours (which would normally be the case all summer), it
winds it to the end and back. (One thing I didn't check but
was intending to was that it actually got to the end and
operated the microswitch.)
[email address is not usable -- followup in the newsgroup]
Andrew Gabriel presented the following explanation :
My boiler is in a kitchen cupboard, which makes it noticeable when it
is quiet in the kitchen. I noticed it this morning again, at 09:45. It
is set to allow CH, but the stat is set to 15C so it should not be
called in this warmer weather at all. The last time it was called to
provide any heat was yesterday, for HW - I had a bath, then Jean had a
bath in the afternoon and it was timed to come on heat HW at 16:20. So
probably there would be no call for the boiler to fire any later than
I have not read the manual thoroughly, there is a lot of it, but I
didn't spot any mention of it doing an occasional purge, so I have
emailed Vaillant to ask them about it.
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