Follow up to central heating problem
Lawrie Davidson
problem of radiators heating up when only calling for hot water. It
does indeed seem like a stuck mid position valve. Can I ask one
further question. The valve is a Danfoss Randall HSA3 and even when
both CH and HW are turned off and the outlet pipes from the valve are
cold, the white plastic top on the valve is really hot. Is this normal
and should I get it looked at quickly. Also what is the lever on the
side of the valve marked MAN and AUTO for ?
Thanks, Lawrie
Roger Mills
I don't think the acuator should be hot - but these thinks are a bit of a
law unto themselves!
One thing to try is to power it off completely - by turning off the FCU
which powers the whole system rather than just turning HW and CH off at the
programmer. This can sometimes reset it when it gets 'confused' - and you
might find that it works ok when you turn it on again.
The lever enables you to move the valve to the mid position (but not all the
way to the CH-only position). It's useful when filling the system, since it
allows water to flow into both circuits. You can also use it in an
emergency - if the actuator motor fails - to get some hot water to the
radiators (but only whilst the HW circuit is calling for heat. It can also
give you an indication of the position of the valve. If you can only move
the lever slowly against the resistance of the gears and the return spring,
the valve is in the rest (HW-only) position. If the lever moves freely with
no resistance, the valve is at the mid position, or beyond. [It should
definitely be at the HW-only position when you power it down at the FCU. If
it isn't, you've got a problem!]
--
Cheers,
Roger
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spamlet
"Lawrie Davidson" <irisa...@onetel.net> wrote in message
news:0bfb776f-c168-4e70...@5g2000yqj.googlegroups.com...
Well at least you know the actuator motor isn't burned out yet!
The explanation is probably in this quote from the UKdiy FAQ:
"In the "both off" state, the system wiring results in grey being live. If
the valve happens to be in the A+B or B position, SW1 will have been
operated, the motor will be fed with AC, and the valve will wind to B and
stay there (although the orange boiler output will not be live). This is a
fly in the ointment for this valve configuration: the motor can be left
consuming power and wearing out its hot windings unnecessarily (the spec
says the valve consumes 6W). This will not happen in the summer though, when
heating is never selected: SW1 will be at rest, and the valve will sit at A
un-energised."
Here's the full article explaining how the actuator works:
http://www.diyfaq.org.uk/plumbing/controls/midpositionvalve.htm
Turning the HW on should drive the valve away from this mid position and
turn the motor off. Until you try to run it with CH on its own: after which
it will probably get stuck again.
Still not quite sure if it's really the valve or one of the actuator
switches that has got stuck though (The article does actually note the
operation "has obviously required quite a bit of lateral thinking to conjure
up".).
If, as another contributor said, you can't turn the valve to all three
positions with the actuator taken off, then you need a new valve - usually
meaning at least partial draining of the system unless you have some handy
isolator valves fitted. If you can turn the valve, then you need a new
actuator - in my view the most likely thing to fail (And, yes, I have
wasted time and money changing a valve, only to find there was nothng wrong
with it before now...)
S
Harry Bloomfield
> The valve is a Danfoss Randall HSA3 and even when
> both CH and HW are turned off and the outlet pipes from the valve are
> cold, the white plastic top on the valve is really hot.
> Is this normal and should I get it looked at quickly.
That is heat from the actuator motor, which runs much of the time.
> Also what is the lever on the
> side of the valve marked MAN and AUTO for ?
The manual position allows you to bypass the motor system if it has
failed and get the heating to work.
> Is this normal and should I get it looked at quickly.
These actuators are a poor design and fail regularly. Undo the two
screws which hold it down on the valve, after noting which way it goes
back. Lift the actuator off and check you can easily turn the valve
spindle (the half moon shaped part on top) - It should be possible to
turn it 360 and almost manage to turn it with your fingers. If you can,
it is fine, so go out and buy another actuator head, then fit it in
place of the old one. Just four wires to reconnect, but carefully note
what goes where.
It might be worth getting two heads, so you have a spare ready to fit -
they are such a common point of failure. Expect failure every 12 to 36
months. They cost £30 to £45 each, but you can buy spare parts for them
if the body is sound. You can get replacement motors for £14 and
replacement microswitches for £1 each, if you fancy trying to repair a
failed on for a spare.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
Harry Bloomfield
> I had endless failures with HSA3s, always the microswitches after not many
> months. System was re-jugged to use HSA2s (2 port version) which lasted in
> years what the HSA3s had in months, eventually leaking round the spindle.
Definitely a round tuit for me.
>
> Whilst using HSA3s I kept a spare head and swapped, and then changed the
> micro switches at leasure for the next time.
That is what I have done for years. I even made the swap a bit easier
by making them a plug-in at the main junction box.
spamlet
"Harry Bloomfield" <harry...@NOSPAM.tiscali.co.uk> wrote in message
news:mn.ca237da42f...@NOSPAM.tiscali.co.uk...
> Lawrie Davidson used his keyboard to write :
>
> (the half moon shaped part on top) - It should be possible to turn it 360
> and almost manage to turn it with your fingers.
Can't speak for all possible designs Harry, but the two kinds I have seen
either have a ball on a stick inside, or a rubber triangle. Either way the
flap or ball will only move less than 180 degree, unless the ports are going
in at very odd angles! I would think the shaft would only turn 360 degree
if it is broken inside.
S
Harry Bloomfield
> Can't speak for all possible designs Harry, but the two kinds I have seen
> either have a ball on a stick inside, or a rubber triangle. Either way the
> flap or ball will only move less than 180 degree, unless the ports are going
> in at very odd angles! I would think the shaft would only turn 360 degree if
> it is broken inside.
We have had two generations of 3 port valves and both rotated for the
full 360 degrees. 1 pipe in from either side (horizontal) and the third
entering from below (like a T), with the actuator mounted above on the
valve spigot.
spamlet
OP better be careful.
S