12 volt DC 3 way mid position valve (central heating)

[CampinGazz]

i'm fitting a home style heating and water system to my motorhome, a 12 volt eberspacher 5KW water boiler, a 20 litre twin coil calorifier (hot water cylinder with an extra coil to heat from the engine) 3 radiators, digital programmer, tank and room stats, and hopefully a 3 way valve to select hot water, heating or both to be heater when the boilers running.

But i just can't seem to find a 12 volt DC powered 3 way valve, the mid position type that's fitted to 99% of home central heating systems,

does anyone know where i can get one from?

and i know all about inverters, and that's not an option to run a simple valve, as it'd have to be powered all the time, and my 2 inverters in the van pull a fair bit of current when ideling, and take a few seconds to power up due to self checks (ones a 1600 watt modified sine wave that powers the microwave, central vacuum system and any phone chargers etc, that high a power uses about an amp when no load is being pulled, the others a 300 watt pure sine wave inverter that powers only the washing machine, being pure sine wave it pulls even more power than the big inverter when left powered up and not being used, and takes about 10 seconds to turn on due to complex self checks of the entire system)

So i really need a 12 volt powered 3 way valve, but where are they hiding???

[Harry Bloomfield]

CampinGazz used his keyboard to write :

12v 5Kw sounds to be rather a large supply cable (?)

You might have better luck finding a pair of simple 12v solenoid valves instead of the three port.

[Sparks]

That is waht I thought at first, 416A is rather large! I expect he means it is a gas boiler (LPG) with 12v controls though..

Sparks...

[CampinGazz]

yes, it's 5KW heat output, powered by diesel, the 12 volts runs the combustion blower fan, controls and water pump,

[Matt]

eberspacher = diesel or petrol or lpg fuelled, NOT 12v! Commonly used by truckers and yachties.

[Sponix]

Perhaps they are used on boats? Worth trying a chandlery.

sponix

[Mark]

Don't think you can get these, Im pretty sure my BIL Winnebago thing uses two 12v 2way (On/Off) solenoid type valves to control the CH/HW. And S-plan plumbing

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[Bob Mannix]

I suspect you are correct. The "normal" three way valves as used in CH systems are stalled in some positions and this is easier to achieve with the AC synchronous motors with which they are fitted. I think this sort of operation would be a lot harder to achieve with a 12V DC motor, which is probably why you can't find them. As another poster has suggested, the use of 2 12V solenoid valves and appropriate controls would be a better bet, although this arrangement could fail with all shut (which a 3-way valve can't) giving rise to potential hazards. It might be better to employ one solenoid valve and put up with the much less flexible options of "Water only" and "Heating and water", putting up with the lower flow round the heating circuit (but it's only three rads). There is always a water path open whatever valve failure scenario occurs.

[Mark]

I *Think* on the Winnebago one valve is N/O (HW) and the other is N/C On energising they switch state, so even with power off there is always a water path open.

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[Roger Mills (aka Set Square)]

You'd probably stand more chance of getting 12v on/off valves - rather than a 3-port valve - and then use 2 of them, as in a domestic S-Plan rather than Y-plan system. I don't know about secondary contacts which close when the valves open - you may need to use relays to create that feature.

[Bob Mannix]

True, but that is only one failure mode. It's still possible for a single stick shut to result in no water path. It is physically impossible in a 3 way valve.

[Sparks]

You can get 12v valves like this too :-)

Sparks...

[Mark]

If you get an irritable urge to hit the Follow-up button at least read the rest of the thread first. Its 12v that we are talking about !

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[Sparks]

I did, maybe you should do so.

The last poster said he *thought* this was the case - I have used 12v N/O and N/C valves, so I know they do exist, and are easily obtainable here in the UK.

Sparks...

[CampinGazz]

can you give me a pointer to them please??

they need to be able to work with 82 degree C water going through them all the time, be continious rated, and not cost the earth... seems i can get what i want for a few hundered quid, or some that dont say they are rated for hot water for 15 quid,

[Sparks]

I bought some from

- I just called them and they were able to supply me with small quantities (for order was for 1, to see if it was what I needed)

Sparks...

[Andy Hall]

Don't forget that there is Honeywell S-plan. This consists of two port valves, with one normally being open at a time.

A microswitch in each is used in the path to fire the boiler such that unless at least one valve is open, the boiler can't fire.

Whether this exists for 12v valves, I am less certain, however a look through the web site of Sauter may reveal something suitable.

products are orderable through PlumbCenter or ClimateCenter

[Andy Hall]

Even so, this is not quite as foolproof as two port S-plan valves because the latter have a mechanically linked microswitch which can only operate if the valve really is open; I suppose unless the contacts weld shut or something.

With a relay across the coil of a solenoid valve, you don't know if the valve coil is open circuit or the valve stuck.

Presumably a boiler should protect itself in case of pump failure so one would hope that it doesn't all go bang or I suppose another way would be to include a flow switch and use that to control the boiler.... That would be fail safe at least (unless its contacts welded shut of course.)

[Roger Mills (aka Set Square)]

I was aware that it's not as good as a valve with built-in microswitches, and should perhaps have made that limitation more explicit. Possibly the heating system in a motorhome is left unattended less than that in domestic premises - so you would quickly become aware of a problem - I don't know.

You could always plumb an automatic by-pass valve in parallel with the heating valve - which would open in the event of the boiler/pump running when both valves were closed.

[CampinGazz]

yup, the eberspacher heater is full of safety devises, i'd imagine the pump would stall or run slow if it had no where to pump the water, and the heater shuts down and flashes a fault code if the pump runs at a lower speed than it should because it thinks there's a blockage.

it's also got an overheat protection of about 95 degrees C, where it shuts down again and won't re-start untill the fault code is cleared and hopefully the fault is rectified as well.. otherwise it'll just shut down again, 3 shut downs and it locks out needing a reset with the programmer.

of course all this computer control means there's more to go wrong in the first place with all these sensors, but at least it's got plenty of safety things.