Sunvic 1801 and Unishare 1901 - explosions and damage caused in part by slight ingress of water from leaking valve spindle seals - and also by a capacitor shorting on a link wire.
The modern range of Sunvic motorised valves includes those that have an electronic circuit board incorporating both low (24 volt) and higher (240 volt) tracks in close proximity. As is usual practice, the recommendation is not to install the actuator below the valve - to avoid filling the casing with water if the valve spindle leaks.
However, in these actuators (types 1801 and 1901), ingress of even a small amount of water seems to cause catastrophic electrical failure.
I have successfully modified 1801 actuators to make them work again in systems where the valve spindles are leaking a little - ask for details. Unfortunately, 1901 units cannot so easily be modified and a complete new valve assembly may be required.
Most of the pictures on this webpage are of an 18 month old Unishare 1901 actuator. Damage includes exploded smoothing capacitors, areas of burnt printed circuit board (pcb), vaporised pcb tracks and extensive corrosion of spade terminals. The actuator failed in such a way that power was supplied continuously to the motor - which overheated as a result. Amazingly, the microswitches were still working satisfactorily. One of the reasons why the damage is so extensive seems to be a poor design layout of tracks on the pcb.
This actuator had been installed in a vertical plane (which is a recommended orientation) and with the cable outlet to the bottom. It is explained below that because of the internal layout of components, this means that any water entering the housing inevitably finds its way onto the circuit board - where it can short out both 24 volt and 240 volt components. Indeed it can link the two together.
It is difficult to say exactly which components failed first - but as with other Sunvic actuators that have been examined, the benefits of having a substantially 'flameproof' outer casing are obvious. It is probably advisable never to smother motorised valves in clothing - yet this is quite common if only because they are often installed in airing cupboards.
Whilst some damage resulted from water leaking directly onto the circuit board, most of the damage may have resulted from long term immersion of the circuit board and associated components in the high humidity atmosphere that may have formed inside the casing. However, similar but not so extensive damage has occasionally been seen in other actuators of the same type, leading to a suspicion that the quality of the pcb board material may be partly to blame.
In another unishare actuator - again only about 18 months old, poor quality control during manufacturing resulted in the casing of one of the smoothing capacitors contacting a mains voltage link wire. The capacitor exploded, part of a pcb track vapourised and the actuator stopped working properly. Amazingly, all that was required to repair it was to replace the smoothing capacitor, reroute the link wire, repair the blown pcb track and (probably unnecessarily) replace a zener diode. This actuator provided an unusual example of how mains voltage was caused to contact the low voltage components with damaging but quite minor consequences.
|Electronic component damage
included an exploded smoothing capacitor (centre right of picture) - this was loose inside
the actuator, having become detached from the pcb presumably as consequence of the
explosion. This in turn may have been caused by mains voltage (240VAC) being applied
across the capacitor as a result of breakdown of the pcb. The other smoothing capacitor
(left of picture) has ruptured but not to such a spectacular degree.
These actuators have a set of three microswitches as well as two sets of X2 voltage dropping capacitors and bridge rectifier circuits, one to operate each of the relays.
The electronic circuitry is convoluted despite being intrinsically simple and the whole design is quite clever.
Yet in practice it seems to be acutely sensitive to water ingress, inherently susceptible to early electronic failure (because of the use of X2 suppresser capacitors as voltage droppers) and let down by suspect quality pcb design and construction.
Apart from that - it shows real promise!
|The wiring loom is connected to
the circuit board by push-on spade connectors - these are obviously steel (which is
cheaper than brass).
Although only 18 months old, the connectors are extensively corroded owing to having been immersed in high humidity as a result of a small quantity of water leaking into the unit.
The corrosion rate would have been increased because of the mixed metal combination - steel connectors pushed onto brass lugs.
The crimped copper wires can be seen on the connectors serving the blue and grey cables.
|Catastrophic failure of the
printed circuit board (pcb) in a Sunvic Unishare 1901 valve: this is the board in its 'as
received' condition .
There are two areas where the printed circuits have vaporised or burnt away - one at the top of the picture (in an area carrying only mains voltage) and (to the middle right of the picture) where there are 24volt and 240 volt pcb tracks in close proximity.
The degree of corrosion is quite remarkable for a unit that is only 18 months old - it was manufactured in late 2008 according to the date stamps and failed in December 2010.
One of the BZT 24 volt zener diodes (centre right of picture) is so covered in corrosion products as to be unrecognisable.
|A mixture of smoke and
explosion damage including possibly vaporised pcb tracks, recorded on the inside of the
The housing itself shows signs of distortion - maybe a consequence of overheating as a result of the motor running continuously - itself a consequence of the electronic and pcb failures, which in turn resulted in part from water ingress.
|Water entering the actuator
from a leaking valve spindle drips behind the red gear wheel and down onto the U shaped
plastic boss that forms the location plate for the printed circuit board.
Because the board is secured tightly to the location plate, water is channelled by the U shape onto the top (component side) of the circuit board where it can either evaporate or act directly to short out both 24volt and 240 volt components.
The rust stains are from the steel screws used to secure the microswitches (and hence the circuit board) into position.
It would seem to be advisable for these actuators only to be positioned above valves, so that water leaking from a valve spindle would be denied any opportunity to affect the electronics.
It is also advisable for vertical pipework to have the actuator positioned with its cable pointing upwards - but 3 port design MUST be installed with its cable to the PORT A side of the 3 port valve (central heating side).
|Close up of part of the failed
pcb after cleaning.
This board shows extreme examples of a type of degradation that has been seen in other Unishare actuators. Where there is a high voltage gradient (voltage per unit length between adjacent tracks) the pcb material seems subject to early breakdown and carbonation. This leads to current passing across and burning out the pcb material completely, as well as leading to a possible electrical connection between tracks that should be isolated from each other.
The example of burning at the top (highlighted in red) is extreme - the pcb is burnt nearly through its depth and had perforated at one point. The purple lines show the three sets of microswitch connections.
The connections in the black circle are 24 volt, yet mains voltage has tracked across in two areas (shown within blue circles) causing a capacitor to explode and the bridge rectifier to be short circuited. The areas in blue are where 24 volt and 240 volt tracks come quite close to one another.
Amazingly, the microswitches were in good
electrical condition. The zener diodes also often survive when boards are damaged in this
|Close up of the large area of
failed and burnt pcb after cleaning with water, detergent and a stiff nylon brush. Similar
damage is sometimes seen on the pcbs of boiler control circuits, in areas that carry
higher voltages (mains voltage or above).
There may be a fundamental design weakness here - low quality pcb boards may simply not be suitable for use where closely adjacent tracks carry substantially different voltages. Water vapour within the unit may in time soak into the fabric of the pcb degrading its electrical resistance and leading to current flow. However, water ingress cannot be blamed in cases where no valve spindle or other leakage was evident - therefore the pcb quality and or track layout and design seems to be suspect. This circuit board was only 18 months old.
|The motor on the left had been operating for many hours as a result of the damage to the pcb shown above. Surprisingly, it was still working and this included a satisfactorily operating 'kickback' mechanism to ensure uni-directional rotation.|
|A Unishare circuit board as it
I would always recommend that domestic hot water and central heating systems use 2 two-port valves rather than a single Unishare of this type.
Two-port valve actuators are easier to repair, it is easier to diagnose faults and the valves themselves can more easily be operated manually if the actuator has to be removed for repair.
|The areas highlighted in purple
and including the zener diodes operate at 24 volts, and serve to control the 24VDC relay
The mains neutral line is shown blue - this connects only to one side of the 240VAC motor and to one pin of each of the bridge rectifiers. All other tracks carry mains live voltage at various times during cycles.
The motor live connection and tracks to microswitches are shown yellow: the motor can receive power from many different places on the board, depending on where in the cycle it is and the state on incoming signals.
At three points, the purple areas come very close to tracks carrying mains voltage: these are shown by the small red circles. The two areas to the right of the picture seem prone to burning through - especially the one shown by the thicker small red circle.
At the top of the board there is another design problem: within the two concentric red circles the linked microswitch pins are extremely close to another track carrying mains voltage. The next picture (below) shows this area in close-up.
|There is only a fraction of a
mm clearance between the heavily soldered pins of the microswitches and the track that
runs above them. If at some times during cycles there is mains voltage across these areas,
then the voltage gradient may be too high if the board is even slightly damp, and current
may track across.
When this area does burn through (as has happened on the board that is the subject of most of the photos on this webpage) the motor may receive power when it should not and so it runs continually - and overheats.
The track right at the top of the board is thicker than most because it carries the full load current to the orange wire - and it is this that tells the boiler to fire. In these 3 port valves, power supplied to the white wire (asking for central heating) flows via a relay contact and a microswitch to the orange wire.
Failure of either relay or any of the operative microswitch points (5 out the possible 6) can cause actuator malfunction. However, intermittent failure is usually owing to capacitor problems - which are much easier to diagnose and remedy!
|An unusual fault in a Unishare
actuator that was less than 2 years old.
The pcb was manufactured with one of the link wires standing proud of the pcb. This link carries mains voltage to the motor.
When the motor was screwed into place during assembly, the smoothing capacitor was compressed on to the link wire.
The red circle shows where the capacitor was pressed down by the motor casing.
The green circle shows where the link wire was eventually forced through the insulating plastic sleeve around the capacitor, thus imposing mains voltage on its metal outer case. In turn the whole motor body may have become 'live' but this seemed not to have caused any lasting damage.
As the capacitor was destroyed its casing ruptured, leaking chemical by-products - these can be seen as a black deposit on the top of the capacitor.
A pcb track on the other side of the board also failed owing to the sudden imposition of mains voltage onto a part of the circuit that was designed to work at only 24 volts.
|This photograph shows more
clearly how the link wire (L1) had been installed - protruding well above the circuit
In all, it is an unusual example of poor quality control - if a whole batch of Unishare actuators have been manufactured with the same fault then many if not all may be expected to fail in a similar manner.
This actuator was manufactured in 2009 and failed in January 2011. A manufacturing fault of this type may cause failure at any time - after a few weeks or many years' of operation, depending on how much pressure is exerted on the thin insulation around the capacitor casing.
|Unluckily for one house owner,
a pair of his 1801 units failed owing to water ingress.
In both cases the circuit boards exploded. One or more of the relay connecting pins were destroyed, thus rendering the units beyond economic repair.
In any case, both circuit boards were breaking down internally with carbonation evident within the thickness of the board. This damage seems to lead to high voltage tracking and subsequently to explosions.
The vaporised metal has been safely contained inside the actuator casing. In the unit on the right, one of the connecting pins has been blown away from the board by the force of the explosion, and its remains can be seen adhering to the side of the casing (top right corner).
These units were 8 years old - many of this age seem now to be failing in a similar manner as very slight water seepage causes dampness within the circuit boards.
|I once experienced at first hand an explosion of a 1901 circuit board.
This had been sent to me for inspection having already been suspected of blowing the
system fuse in a household boiler system.
When connected to a test circuit the actuator had already had several days in which to dry out both in the post and in my home.
Nevertheless upon connecting power to the grey wire
(terminal 4) there was a loud explosion, a bright flash and a 5 amp fuse ruptured. This
event served to illustrate the care needed even in testing these devices. The inside of
the grey plastics housing showed only a tiny tell-tale trace of a previous explosion, far
less evidential than some of the pictures shown above!
|The actuator as received showed an unusually large amount of 'fluff'
inside it (green outline), evidence perhaps if it having been used inside an airing
There is a small amount of telltale discoloration of the circuit board (blue outline) and some corrosion of one of the connecting wires (red circle) perhaps caused by dampness.
The explosion occurred to the left of this picture.
|When relay RL2 and capacitor C2 were unsoldered and removed, the extent of
water damage to the circuit board and the high voltage tracking is evident.
This unit was 7 years old - ample time for a small amount of water seepage to occur from the valve spindle and cause dampness of the circuit board.
The rest, as they say, is history.
|When cleaned up (using an old toothbrush and washing up liquid) a single
track can be seen eaten into the pcb. This is between the high voltage (mains voltage)
side of C2 and one of the low voltage coil connections of RL2.
Extensive 'internal' degradation of the printed circuit board is also evident within the blue ellipse.
This type of damage is routinely seen in 1801 circuit boards also.
It cannot be emphasised too strongly - NEVER operate these devices without their protective covers in place. Even a dry but degraded board may explode and possibly cause a house fire.
When this particular board exploded the accompanying flash was quite spectacular - and not readily forgotten!
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