Sunvic SD2701 actuator

[The Medway Handyman]

Problems with the CH & HW at Handyman Towers.

Water is getting far too hot,although tank stat is turned down, rads not hot enough at times.

Seems to be the 3 port valve (1 in, 1 to tank, 1 to rads)

Having read the fault finding guide on the interweb, I removed the actuator and turned the spindle by hand. The destructions state;

"If power is present on the appropriate wires and the actuator still doesn?t operate as expected, remove it from the valve and see if it motors to the correct positions when off the valve".

But it doesn't say what the 'correct positions' are.

"If it doesn?t, then it?s a faulty actuator. If it does, check the valve spindle is free to rotate using your fingers only. If you require pliers or grips to move the spindle, then the actuator will be unable to turn it".

You can turn the spindle by hand, albeit a little stiff. However, when the actuator moves in the direction of the CH port, it stops half way & clicks.

Sounds like a duff actuator to me, but I don't want to shell out £75 if its the valve.

I assume changing the vale is a drain down job?

[A.Lee]

...

Yes, it sounds like the splines/gears are worn out. Sunvic are branded by other makes too, do a search and you should get one for £30.

[harry]

You should be able to get the actuator motor to move by adjusting the hot water thermostat. Just the fact that is moves is enough you don't need to know it's position. They only move slowly BTW.

Get someone else to adjust the thermostat if you can't see it from the actuator position.

[The Medway Handyman]

It only moves halfway then clicks. Is that right?

[The Medway Handyman]

Got anymore detail on that Alan? £30 sounds much better :-)

[A.Lee]

Ebay turn up the cheapest mostly. Bought a Honeywell actuator for £30 last week, also got a complete 3 port Drayton valve for £40 a couple of weeks ago. It may be Danfoss that are the same as Sunvic. Check the pics to see if they are the same. Here's one here:

Thats the first one in an ebay search, there may be others.

[Harry Bloomfield]

That sounds about right, the click is the microswitch. The microswitches need to be triggered, to show the correct positions for the boiler to fire, so it seems you might have a faulty microswitch indicating a wrong position if the boiler is heating the water instead of the rads. By a new actuator, then check out/repair your original as a spare. You can get the microswitches from Maplins for a pound.

Motors, though yours seems to be OK, can be had for £15.

[John Rumm]

If you mean click repeatedly - like a gear slipping, then no. If you mean there is a single click like a microswitch being activated, then yes.

Armed with a multimeter you should be able to follow the logic through using :

and

[The Medway Handyman]

It's repeated clicking.

The spindle is 'D' shaped. The actuator turns it 180 in one direction, but only 90 in the other when the clicking starts.

Now I know what I'm doing tomorrow night :-)

[The Medway Handyman]

It look identical, cheers.

[John Rumm]

Sounds like a knackered gearbox then...

The shaft itself only rotates through a relatively narrow arc - say 30 deg or so...

Looking for the signal from the microswitch is one way of knowing if its reaching full travel.

[harry]

There may be a fault in the gearbox. (Teeth stripped?)

[SAUSAGE]

When they only go so far but keep clicking it is always a duff microswitch. Just replaceboth of them while you have the thing open. It is nothing to do with stripped teeth or the gear box. The contacts in the micro switches need to be switching off and on the boiler and the pump which are highly inductive. In a nut shell the contacts are going to spark and get a hammering. One solution for a longer life is to fit supression capacitors across the contacts, problem is fitting them in.

[chop]

You are only 9 years late, you silly sausage.

[John J]

[Brian Gaff]

Yes I thought that, but it also begs the question as to why suppression is not fitted as standard in the first place. Brian

[Animal]

replying to the wrong realm too.

[Harry Bloomfield Esq]

Because it's not needed, they don't 'spark'. The cam hits the switch, operates the contacts, which are then designed to simply stall the motor at that position.

I think the poster assumed the micro-switch caused the motor to continually switch on and off, winding and unwinding on the spring, constantly switching the microswitch.

[SAUSAGE]

They are not fitted because there is no room in the enclosure to do that, plus Sunvic don't care what happens after the six month warranty runs out. Harry, they do spark. The CH or HW call signal passes through them to actually fire the boiler and pump up. The mid position is held by feeding the motor with half wave mains through the diode and resistor, and a reduced demagitising signal on the other half of the mains with another resistor. I have never indicated that the microswithes are designed to switch the motor off and on in the mid position. I was trying to point our that when switch number 2 fails, the motor gets no half wave mains from the diode. It then spring returns back until switch number 1 kicks in again and starts heading back to mid position, and so forth. This is when people get the classic clicking situation coming from the cam constantly operating switch number 1 . The last phone call I had with Sunvic indicated that their engineers no longer know what the diode and resistors are actually for which says everything about them. The last call I had with 'Synchron' indicated that the motors were never designed for this purpose and accept no responsibility. My final solution : Use the microswitches to operate 12 volt relays which then do all the switching externally, with higher current rated contacts (again with capacitors fitted). Ditch the mid position altogether and wire it so that the central heating position can only happen if the hot water tank is up to temperature. It still does not get the motor out of the situation where it is still running all the time in the CH position with no where to go, but does solve all the problems with the underated micro switches for inductive loads and the motor getting magnetically locked in the mid position (another fault which happens over time). If you are sticking with the original design, then change the 270K resistor to 220k 1W and connect it to the motor from a constant live feed. That way it is constantly being demagnetised even if the boiler is off.