Sunvic motorised valve failures

Failures of SUNVIC motorised valves including those with actuators SZM 1801 and SDM 1901 Unishare valves (and spring return types) - why they fail and how to repair them (now including supply of spare parts!).

This part of the SeeRed website details why Sunvic motorised central heating valve actuators of a particular design often fail to operate correctly. The main text applies to both modern two-port and three-port (unishare) valves. These all have a similar design of electronic circuit and regularly fail in a similar manner.

The popular Unishare three port valves are particularly prone to failure but can be repaired quite easily. The two port designs simply fail to open reliably a few months before they fail completely. Again, repair is usually straightforward. Spring return valves can also be repaired but often at greater cost. Fortunately, it is not necessary to drain the system to effect repairs - all that needs to be removed is the valve actuator.

Failure can lead to low room or domestic hot water (DHW) temperatures. This in turn can lead to other components such as thermostats and programmers being suspected of being faulty. Hundreds of pounds could be wasted in replacing components unnecessarily. A less common fault in Unishare three-port valves can lead to excessive hot water temperatures.

More seriously, faulty central heating controls can leave elderly people vulnerable to the cold. Failure of these Sunvic actuators may be expected to be intermittent, at least for several months if not longer, as electronic components gradually degrade. Old people may not be believed when they complain about being cold - because when relatives or health visitors call, the heating system may be working satisfactorily again.

This part of the SeeRed website is being made available free of charge in the public interest. A similar section dealing with repair of caravan gas heaters has been available for a small charge for some years.

********* REPAIR SERVICE! *********

A repair service for many types of Sunvic and other makes of valves is now offered: a Ł10 or Ł12 repair (including UK P&P) being better than a new valve actuator. For queries, email the SeeRed author: stevewozniak42@hotmail.com.

This repair service is usually also offered directly from ebay and can include replacing faulty microswitches, which is a less common cause of failure. Two port valve actuators are repaired for Ł10 (return P&P included to UK), three port types for Ł12 (also including return postage to UK).

Repair of some types of spring return motorised valves is also offered on the same terms - for the moment, the rest of these webpages deal only with modern Sunvic motor-on motor-off (MoMo) valves including the popular Unishare type.

Please note I do NOT currently hold stocks of valve actuators. To operate your system without the valve actuator in place can be a little daunting if you are not experienced in electrics and central heating. Some guidance on how to operate simple systems without the valve actuators in place is given below. However....... Don't meddle with electricity unless you know what you are doing. You could kill yourself. Also, do not open actuators unless you are competent to do so - the high voltage capacitors inside some types can retain charge even when the unit is wholly disconnected from the mains.

Supply of spare parts for Sunvic motorised valve actuators.

Owing to demand, I am now supplying spare parts for Sunvic motorised valves but ONLY the capacitors that routinely fail in their innovative range of MoMo valves (1801, 1901 and similar types). These capacitors can be supplied for Ł1 each, plus a P&P charge of 50p (to UK) - so one capacitor will cost you Ł1.50 and two will cost you Ł2.50. Email me for overseas prices please. NO OTHER SPARE PARTS ARE STOCKED. The capacitors supplied will be X2 rated of a similar spec to the originals. They will be 330 nF rather than the 220 nF that Sunvic used in earlier batches of actuators - before they discovered that many of their valves were failing so prematurely. Be aware when fitting these that the old units may have retained some charge - therefore discharge them before unsoldering. Also, if repairing an early valve with a 220nF capacitor, you will need to fit a zener diode to limit the relay coil voltage if you fit a 330nF replacement.

In purchasing these spare parts you MUST be aware that repair of these valve actuators is (of course) not recommended by Sunvic. However, given the simplicity of repair for anyone well versed in soldering of electronic components, DIY repair is a feasible proposition, provided you are wholly competent in dealing with mains electricity and hobby electronics. If you don't meet these criteria then get someone who is a 'competent person' to remove the valve for you and make the system safe, then post it to me for repair. Sometimes, the zener diodes that are connected across the relay coils have been found to be almost 'short circuit' - in this case the DC voltage across the relay coils may be as low as 0.2 - instead of 24.

All legal liability for any incompetent repair rests solely with the person who undertook the repair. If you don't know what you are doing, then don't do it!!

Full electronic circuit information and analysis of Sunvic claims will be added soon. It is noted that the Sunvic company has failed to respond to emails questioning the reliability of products that are described in Sunvic sales literature as being very reliable - my experience is a 100% failure rate in three years! Unishare three port (mixer) valves can fail in under three years - I have repaired several that are between 1 and 2 years old. There is a good technical reason why these popular Unishare valves are proving to be even less reliable than their two-port alternatives - this is explained here.

The detailed emails I sent to Sunvic on 27 Jan (resent on 9 Feb 2007) are here

In an email to me dated 30 October 2007 (click here) Sunvic claimed never to have received my emails. They were certainly received by the persons to whom they were sent "bcc" (including to my own in-box). It would therefore be truly remarkable if Sunvic didn't receive at least one of them - as can be seen, each was sent to two valid Sunvic email addresses.

A selection of emails received from consumers who have suffered failures of Sunvic valves is here.

Important safety notice: This part of the SeeRed website DOES NOT necessarily apply to combination boilers - do not alter any part of combination boiler systems or pressurised hot water systems without seeking advice. It is assumed that the valves in question are used with a typical traditional UK boiler with an open vented hot water cylinder for stored hot water and radiators for central heating.

Whilst repairing some types of Sunvic valve actuators (and many other makes) is an easy job for anyone versed in electronics, inexperienced people should not attempt this work. Some skill in soldering is required - and remember these are mains operated devices. The usual precautions should be taken when removing a unit from the mains wiring - including switching off the isolating switch-fuse that should control the entire heating system and removing the fuse. In addition, check that the system really is 'dead' after removing the fuse - I have known houses in which live and neutral lines have been reversed even at the main fusebox!

Also, remember to make a careful note of which colour wire goes where - and if you are removing two valve actuators, which wire from each actuator goes where! Do NOT attempt this work yourself unless you are experienced in mains wiring. With systems using two two-port valves (one for central heating, the other for domestic hot water control), you may find that two orange wires, one from each valve actuator, are joined together - this is normal. The two grey wires may also be joined (again one from each actuator) - these are merely the permanent mains feeds to the two-port actuators, similarly the two blue wires (mains neutrals). The two brown wires must be replaced in their correct positions - or you will end up with the central heating controlling the dhw and vice-versa! Typical wiring diagrams are shown in the Sunvic catalogue (750k pdf file, allow time to download) - the diagrams are on page 17. Just be sure you study the right one!!

The wiring of many central heating systems in the UK is undertaken to an appalling standard (typical of the UK building industry) so be prepared to find shoddy work that needs rectifying.

If sending a two port valve actuator for repair, the central heating can be left in operation by turning the valve spindle to the 'on' position and using the time-switch or programmer to control room temperature in a crude manner. However, it is also necessary to 'con' the boiler into thinking the valve actuator is still in place and ordering heat! This can be done by temporally linking together junctions within the wiring centre of the heating system - but again this may be fraught with problems because (in my experience) so many are wired to a poor standard. Non-technical householders should not attempt this work themselves. It is a matter of linking together the two terminals to which the BROWN and ORANGE wires of the valve actuator were originally connected. This has the effect of kidding the boiler electronics that the system is asking for heat to be supplied.

The way two-port actuators work is as follows: The BROWN wire supplies live (240 volts) from the relevant thermostat to order the valve to open when the thermostat requests heat. The valve actuator should respond by opening the valve and then signalling to the boiler and pump to switch on - it does this by supplying 240 volts (live) to the ORANGE wire.

If the Sunvic valve actuator controlling the dhw supply has also failed the dhw can of course be operated also but the stored water temperature will approach that of the main boiler thermostat (because the valve will no longer be controlled via the cylinder stat). In these cases, to avoid the risk from scalding, turn down the main boiler thermostat to about 55C. The valve can be closed manually whenever it is desired to stop heating the dhw. All these procedures require some knowledge and competence and, once again, do not meddle unless you understand what you are doing.

If the boiler and plumbing has been installed correctly (famous last words for the UK plumbing industry!) and with a bypass loop, there should be no problem in closing both dhw and ch valves manually if you wish to control the system in this way - the boiler will then cut out on its own thermostat and/or overheat stat and the pump should run until excess heat has been dissipated via the bypass loop. Again, there are many examples of poorly installed plumbing systems in the UK, so ask an expert (if you can find one!) to check if you are in any doubt about operating your system without the valve actuators in place.

Three port valves:

Three-port valves operate in a similar manner but the wiring is different and many valves are never installed properly by typical builders and plumbers in the UK - again, in my experience! Some other types of three-port valves (not the Sunvic type discussed here) are quite complicated internally and are more difficult to repair or test.

To operate the system without a three port actuator in place can sometimes be accomplished by very carefully turning the spindle of the three port valve a little bit with a small pair of locking (molegrip) pliers and wedging it in an open position. In its 'closed' position it will supply only dhw. However, you need to rewire the control panel as well - which would be dicey if you don't know what you are doing. Supplying 'live' to where the orange wire from the valve was connected generally enables the boiler to light up and the pump to operate but there are issues of how hot each circuit will get if it is not properly controlled - so turn down the main boiler thermostat to about 55C. Generally the orange wire is made live within three port valve circuits when either the dhw is required or the valve is instructing the system to provide central heating. But remember - on your own head be it! Don't meddle with electricity unless you know what you are doing. You could kill yourself.

My personal recommendation for standard domestic heating systems has always been to use two two-port valves, rather than one three-port valve. The much older design of Satchwell Sunvic 'Minival' two-port motorised valves were renowned for their long trouble-free life - I have some that are 30 years old and they are still working perfectly. Again, the appropriate wiring diagrams are given in the Sunvic catalogue.

	A view of the motor unit SZM 1801 as used on a Sunvic two-port valve. Similar problems occur within Sunvic three-port Unishare actuators. Indeed, the Unishare design may be even more prone to early failure than are two-port designs. Similar motor control electronics is used within three-port Unishare valves, but the components may be 'live' for longer, and so fail sooner. This is all deeply disappointing because the basic design that lay behind this innovative range of valves is sound - they are a direct wire-in replacement for spring return valves that are a common feature of many domestic central heating circuits. Spring return valves can fail via motor burn-out because the motors are energised all the time the valve is required to be open - but they generally last much longer than these newer Sunvic designs! You can easily tell if a Sunvic valve of this type is 'open' or 'closed'. Just look for the 'flat' on the red gear wheel - a good design feature. With Unishare valves, the flat denotes the mid (mixed) position. Removing the actuator head (the part shown here) could not be simpler - just follow the instructions on the Sunvic leaflet (click here)
	View of the motor unit of a two-port valve, gear wheels (red) and the light blue capacitor which has proven to give problems. This is an X2 rated capacitor and replacements MUST be of a similar specification. X2 capacitors are usually used for suppression of high frequency voltage peaks across 240 VAC lines. They are often used in situations where failure of the capacitor might cause a fire - these capacitors are designed to fail-safe, although some problems apparently still occur because their inherent self-healing characteristics can become compromised. Where failure of a capacitor would lead directly to an electrical shock hazard then an even higher specification Y class capacitor must be specified.
	View of the two microswitches that are operated by the red gearwheels. The electrical relay is on the left - it is a 24VDC type which needs at least 17 to 18 volts to operate reliably. When the light blue capacitor begins to degrade, the available operating voltage drops below that necessary for reliable switch-on, hence the valves exhibit all the symptoms referred to in my emails to Sunvic. I first suspected that either the microswitches or the relay itself was at fault. The equivalent three-port designs are more complicated having two relays and two sets of C1/C2 capacitors and rectifiers, three microswitches but only one motor - all quite clever! Repair and testing are NOT typical DIY jobs - so be warned.
	This is the component that causes most of the trouble. The circuits used in these valves are arguably an inherently poor design because partial failure of either of the two capacitors (or both of them) can lead to a lower than acceptable DC voltages. This is a 220 nF unit from an early valve (late 2003). One of the mysteries is why Sunvic used DC relays. Using slightly more expensive AC relays would have avoided all the problems for a cost excess of a few pence. There may be good reasons why the circuit was designed with DC relays - but I cannot think what they are! Safety note: whilst replacing these capacitors is a trivial job for anyone versed in electronics, inexperienced people should not attempt this. Some skill in soldering is required - and remember this is a mains operated valve. Replacement capacitors MUST have an X2 rating with a 250/275VAC working voltage.
	The zener diode fitted in some Sunvic valve actuators to limit back emf produced by switching off of the relay coil - and to limit forward voltage. This modification (shown rather poorly soldered in this example) may have been introduced by Sunvic in response to valve failures examined under warranty. Ideally this diode would have been incorporated into the original design of the circuit board: this crudely soldered add-on is hardly an advertisement for quality manufacturing! Other diodes found in these valves are physically smaller and are BZX 24 volt types. If the diode fails the coil voltage may rise to about 30 - which may not be too serious - or may drop to 0.2V - which stops the valve working at all!
	A 330nF capacitor is fitted to some valves - this one gave a full 24 VDC across the relay coil - limited by a zener diode. The valve had been sent for repair - but a failed microswitch was the problem. Replacing a microswitch must be done very carefully and using a type exactly equivalent to the original - with a 5amp 250 VAC rating. This is not a job for inexperienced householders! In one Unishare actuator I repaired, a 330nF capacitor was so degraded the relay voltage was only 9.8 - and the unit was less than 3 years old! In another, it was 12 volts after only 15 months. Sunvic appear to have changed the capacitors to 330nF to try to avoid premature valve failures but to little avail - because whole idea of using X2 capacitors to drop mains voltage is suspect. 330nFcapacitors should be used with voltage limiting zener diodes.
	Overheating of PCB tracks in a Sunvic valve actuator that failed because of a microswitch in which the points had become welded together. This failure was caused by excess current: a warm air system heater had been incorrectly wired with full fan current passing through this valve actuator! An installation fault of this type could result in a house fire - so if a component fails in this manner, find out excactly why!! The tell-tale overheating and incipient blistering of the tracks (shown as XXX) is most pronounced on the track connected to the grey wire - which takes the mains live supply into the valve circuits. Discoloration of the track connected to the orange wire was slightly less pronounced.
	The inside of a microswitch that had failed (with contact points welded together). The cause was electrical overloading owing to a fault in a warm air heating system. A 3 amp fuse is usually specified for the isolator of a conventional domestic wet central heating system. The contacts are underneath C. Discoloration at regions X bear witness to overheating. If the contact points were the cause of the overheating (because of high contact resistance) then discoloration would be expected primarily close to the points - yet here it is just as bad on the left hand side. This suggests excess system current as the primary cause of actuator failure.

The full wiring circuits for two-port and three-port valves are included in the following pdf page. This is taken from the patent website describing these Sunvic valves.

pdf diagrams of wiring in sunvic valves (use the zoom feature of Acrobat to view the lower diagram clearly)

Also available is the installation leaflet for Sunvic SZMV series valves and SZM 1801 actuators (allow time to download) - strangely it states that it should not be left with the user - yet these motorised valves are sold by B&Q and other do-it-yourself superstores direct to end users! This leaflet includes the basic wiring diagrams needed by installers.

Other companies in the plumbing industry are more open about their products - for example, Triton showers are often easy to mend because parts can be ordered direct from their website - www.tritonshowers.co.uk - then simply select 'spare parts'. Despite being a user-friendly and very useful website, it has an annoying and slow-to-load hi-tech opening page. Why do companies do this?!

detailed explanation of failure of these valves

why Unishare three port valves are less relaible than equivalent two-port valves

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