"dennis@home" wrote in message
...


"spamlet" wrote in message
om...
A cautionary tale for those investigating probs with their central
heating:

A couple of years ago I finally tracked down a problem that had had
generations of visiting plumbers busy, in frenzied and expensive,
radiator bleeding / pump replacing exercises, all to no effect, at a
friend's house. On careful analysis it turned out to be the motorised
valve actuator (Danfoss) that was the culprit all along.

More specifically, it was due to the pair of crap semi-micro switches
inside the actuator, which perform an elaborate 'dance' with the motor to
wind the valve back and forth between the three port positions. As with
all contacts (like the equally crap ones in mouse buttons), they need
cleaning from time to time, but as these are fixed inside the actuator
assembly they are both difficult to get at, and even more difficult to
clean, or replace.

When the main one of these gets dirty and stops conducting, the valve
stops in the half-way position, and the room thermostat appears to have
packed up, as it 'ceases to turn the 'CH' off' because the water keeps
circulating even when it is apparently set at HW only. There is also
less pump power to the (wrongly shared) CH side, so people start trying
to rebalance/bleed etc. rads, and eventually start blaming the pump. The
last thing anyone seems to think of is the valve actuator for some reason
(possibly because they are so outrageously expensive!).

Back then, initially, I tried to just replace the switches, and did
manage a short term repair after replacing one of them: they are very
cheap even at Maplins. The other one soon failed, however, and the way
it was mounted led to the ancient plastic mounting plate breaking when I
tried to get it off.

So had to grit teeth and face up to buying a new valve/actuator assembly:
and thought I'd better do the valve as well while I was at it (which
also means more expensive/inhibitor, anti knock down the drain: if only
I'd thought to put a stop cock on the outlet to the ch system header tank
while I was at it...)

After extensive reading of these columns and those of the Screwfix
Forum - and some very silly stick from posters who simply would not
believe that a semi-micro switch could ever fail - I decided to opt for
the more expensive Honeywell V4073A valve and actuator which cost me
£60.44 on 15 Nov 2005.

Up until now this seemed to have been a good buy: it had been easy to
fit; had what seemed like a clever ball arrangement rather than flaps in
the valve itself; and a quiet and smooth switching action.

However, I recently began to notice that the CH seemed to be on when it
should not be, so had a closer look yesterday: AND Lo!, inside are just
the same crap switches as in the Danfoss! At first, all seemed not lost,
as these ones were mounted on their own little circuit board, which could
be removed for easy working. Unfortunately, the way they were arranged,
they could not be opened for cleaning until one had been removed from the
board, but once open they were easy to clean the muck off the contacts.

In the Honeywell case however, there was the additional crapness of a
largish 12k resistor which had been dry jointed and was coming in at 20k
as a result, and overheating the circuit board to boot. So I had to
resolder this along with the cleaned switch.

Then the fun really started!
How they assembled the thing I don't know, but the actuating
cams/gears/springs etc, are mounted on such a flimsy metal plate that it
is almost impossible to put the actuator back on the valve and still have
moving parts at the end - the slightest overtightening of a screw, and
the whole thing distorts and nothing moves. "Grrr" - and worse, I said
many times as I struggled in a corner of a tight cupboard with a red hot
water cylinder, for hours to get it to work 'properly'. (Yes I emptied
the tank in the end; and yes; the water in the resulting bath was cold by
the time I was ready for it!)

Once it became mobile, another problem presented itself, in that, on
moving to the centre position from either side, an oscillating motion
tended to be set up with the motor driving its cam against the switch
arms/springs and being bounced rather than operating the switch that
turns it off. Click, click, click, click etc. It may well have been
this oscillation tendency which had burned the switch contacts
'prematurely'.

With much fiddling, I managed to - temporarily I expect - bend the switch
arms enough to correct the bounce, and get it all 'working'.

BUT what a load of crap for what a load of cash!

With this experience, I can say that, if I had had the old Danfoss
(really old) heavy duty gearing, and the Honeywell circuitboard switch
mounting method, I could have at least had an assembly that was easy to
get on and off and reasonably robust; with switches that could be
replaced occasionally. But why are they allowed to get away with still
using the same 'failure guaranteed' switches whilst charging prices which
ought to come with a lifetime guarantee?!

As I would imagine that numerous CH systems must be in a similar state -
unless I have just been extremely unlucky! - with many other people
throwing away money trying to solve 'circulation/air
lock/pump/thermostat' problems, unaware of the nature of these valve
actuators, I thought UK-Diy'ers might appreciate this tip.

With any luck some people reading this might save themselves from wasting
cash test-replacing non faulty parts of their systems.

As for a permanent solution: fraid I don't know.
Anyone know of any valve actuators that work a completely different and
reliable way?
At a sensible price?

I just repaired one a couple of months ago, the switches cost about 90p
from Maplin and take five minutes to fit, they should last for millions of
operations but that's at room temp and they tend to be hot.

" five minutes to fit" !

Honeywell? Danfoss?
Don't know how the current Danfoss are fixed, but if you can unsolder a sw
from the Honeywell board and replace it in five minutes, I take my hat off
to you. Even with a desoldering 'gun' it took me at least that long to
clean the holes.
Also very impressed that you managed to line up the various cams and levers
while under spring tension, enough to get them back over the valve stem. As
it seems to be only the stem itself that keeps them in line I found this to
be very fiddly indeed.

Good luck with your millions of operations: my experience says you will need
to be doing this again in about 2 years.

Regards,

S