My Central Heating Solution using Thermal Actuators

So you should have deployed NO valves to be prepared for a OH crash, ESP or power outage, shouldn’t you ?
Uh-oh, you violated rule #1:wink:

I’m fully with you, also use NCs, probably just looking for someone to share my pain now that Winter Is Coming.


@Confused Just stumbled across this whilst searching for motorised radiator valves to do more or less exactly what you’ve done. Problem is the Amazon link you posted doesn’t work so are these actuators still available? and if so, do you know where?
Thanks, Mike


Have you done a simple Google search for “Electrothermic Actuators”

You’ll find lots of manufacturers make them, with M28 or M30 threads.

I buy 4 wire 230vac versions from a trade supplier.

You can get them in 24v, both 2 wire and 4 wire.

(4 wire have a small switch for signalling when the valve is fully open, which I use to call for heat)

As @MDAR said, they are quite a common item. There should be plenty of local suppliers.

I use the 230v Normally Closed 2 wire versions.

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@MDAR @Confused Thanks guys, even better, the four wire one looks perfect for what I want to do as the auxiliary switches can all be parallelled up to call the boiler.

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That’s exactly what I design into systems, including an interlocking relay so that valves can be cycled once a day during periods of inactivity, without calling for heat.
(A standard feature in a Velbus thermostat)

One tiny word of advice, of all of the units I’ve advised people to install over the last 5 years, about 4 of the micro switches have failed.

I haven’t been told if that’s an over current issue, or a switch warranty thing.

So from now on, I’m going to include a simple small relay to off-load the contact current from the microswitches.

I’ve used these kinds of relay holders with 12vdc, 24vdc or 230vac coils in.

(Some have led indicators to show the coil is being powered)

Hongfa 4 Pole Relay and Base Module 24VDC Coil Voltage | eBay - £6.54 for a 24vdc coil version, they do others, just drop them an email.

My thoughts are that a (~£3) drop in relay has to be easier to change than a whole actuators.

Good luck with your installation

I went for the 2-wire versions. It worked well in my old place, and I’m replicating the setup in my new house I’m in the process of refurbishing, albeit this time I’m centralising the relays with a handful of Sonoff 4ch units, and every radiator will be zoned.

So no Sonoff’s and wires trailing around my rooms :wink:


@MDAR thanks for the heads up regarding the limit switches. Don’t think I’ll have a current problem as I might actually end up using a four channel Sonoff to feed four zone inputs into a small PLC which will send the commands to the valves individually from their own output. The PLC will decide which radiators are on which zones at a given time depending on the season, day and time of day. I could use the PLC to monitor the limit switch and make sure it changes state within 5 minutes of a command or sound an alarm. Early days but that’s my current thinking.
@Confused nice setup.

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Nice! So you would run one of those wires to each radiator around the house with the thermal actuator on it? Sounds like a nice setup! How did you go about running the wires? Did you go under the floors?

Yep, each individual wire is for a room. If there’s multiple radiators in each room (I’ve got 3 rooms with 2 rads), I run a single feed to the room, then tee it off in the room. They run under floor boards, through joists, and going from upstairs to downstairs they run in the walls. Each radiator will have its own thermal actuator.

This is actually just for one half of the house, the other half will have its own set of Sonoff 4ch. The whole house is being rewired, so this gives me a great opportunity to run in all of this cabling, as well as lots of CAT6 and speaker cable. I’ll no doubt do a big write-up once it’s all up and running :slight_smile:


At first thought, this is actually pretty smart… But then I thought again and wondered… Would it ever do any good after all… I guess it requires some ekstra heating starting when the switch turns on or something like that. Without the switch, the heat is already on, cause something already started the actuator (called for heating).
And then, this doesnt seem very smart after all… Or I simply dont get it?

But why?? what called for heating in the first place (and started the actuator) ? I suspect it was the thermostat… So where is the need for this switch. The thermostat will continue to call for heating until the setpoint (temperature) has reached, no matter if the actuator has a switch or not.
As mentioned in the previous message… I dont get it.

@Kim_Andersen In it’s very simplest form, a room stat can be used to switch on the actuator on a radiator. The actuator limit switch can be used to signal the boiler. from this basic principle you can add as many room stats and actuators as you like with the limit switches wired in parallel, any of the actuators will start the boiler but only active actuated radiators would receive heat. The next stage is to substitute all room stats with a more sophisticated control system as previously described.

Hope that explains the concept.

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I get it… I guess there are different ways of doing this…
In our house we have underfloor heating in all rooms, (thats 13 rooms in all). Our boiler is always on and is regulated from a temperature stat. (its in standby when the temperature is reach and not thermostats calls for heating).
Whenever a thermostat calls for heating it will open the actuator and the heating will start to flow through the actuator… All 13 actuators are mounted on a manifold (thats the danish word. I think its the same in english) where the hot water flows through. But only the actuator for a specific room which calls for heating by the thermostat will open. If several rooms calls for heating, then each actuators which belong to the room will open.

In the end, I think the result is the same, but there is no need for a switch in the actuator.
If there is a need for the switch, I believe the switch in the thermostat should be able to cover both situations in your principal. 1. Start the boiler (if needed) and 2. start the actuator. It do take a few minutes for actuator to open fully anyway.

And that is why it is good to rely on a 4 wire actuator. If the boiler runs hot water is a system where all the zone are closed (or the radiators valves off) it can damage the boiler depending on the age of the boiler and the settings. Modern condensing boilers have a setting for this. When I run my heating routine.
The room temperature sensor changes, then
If the temperature is below a certain threshold for that room and the time of day AND the windows are closed then I open the radiator valve.
Because I don’t have the 4 wires actuators, I cheat and call for heat on the boiler 2 minutes after I open one of these actuators. On the other hand. It stop the boiler as soon as I closed the actuator. The actuators take between 2 a 3 minutes to fully open/close.

But, yes, calling for heat on an “empty” system can be dangerous.

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Never ever heard of this… The boiler has a temperature threshold as well as an over-heating valve (security valve) if the pressure (due to the heating) is to big. I dont see how any damaging is possible, unless there are at least two faults.

How many rooms do you have?
If our system was suppose to run this way, the boiler would be started almost all the time, (depending on the season ofcouse). Second, our floor heating is build into the concrete of the floor. It takes quite alot of time to heat up the floor. If it was build on wood, it would take far less time to heat up… On the other hand, floor heating build into concrete will hold the heat much longer after the actuator has been closed.

This is a picture of our heating system (manifold) with all the actuators (sorry about the mess, the picture was taken while I rebuild the solution to be using IHC system):

It’s just bad practice to allow pumps to run into closed systems.

The “safety” values are there as a safety feature, not for daily use.

So, yes, using the microswitches on 2 port valves and Manifold actuators to “call for heat” is a professional norm.

The ONLY Errata to that statement is IF you have at least 1 loop or radiator that is LOCKED open, then and only then is it permissable to run the heat source / boiler / furnace into a system without caring how many zones are open.

With modern modulating heat sources, they will vary their energy usage to counter the return flow temperature.


If the return flow temperature is only slightly lower than the target flow temperature, only a small amount of energy will be used.

I have a commercial client who counts the amount of open valves, to determine how many heat sources are required to meet the demand.

(For example, he normally installs 4 boilers and rotates the usage)

That’s an over pressure valve. All boilers should have them. They fail sometimes but that’s not the issue, the issue here is the thermal loop. The boiler is going to pump hot water in the system and expect a temperature drop after going though the loop. If the radiators or zones in the loop are closed then the water will more or less go back to the boiler straightaway without the expected temperature drop. Modern boilers can cope with that provided they have been told what to expect. Older boiler may get confused by this and just turn off and require a reset.

7 rooms with radiators. The boiler only runs when one of the rooms is calling for heat.

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Just a note.

Velbus thermostats have 8 seperate output states that can be mapped to different output devices

One to many
One to one

So it is totally possible to have a thermostat open a valve and call for heat / cooling / ventilation separately.


An installation only has single contact thermostats, how would the call for heat be isolated from the seperate valve openings.

(That was a hypothetical question, I know the required schematic)

Here’s a thought that I’m going to play with, because I’ve been asked to create radiator control for a client that can’t run any cables.

What if these WiFi smart plugs were wired up to simple 2 wire 230vac Electrothermic Actuators?

(HS100 & WTA & Plugtop <£40)

(Using the TP-Link OH Binding)

And have openHAB2 map a room thermostat to them and a heat call device?

(My client has Velbus glass panels {which have thermostats in} in each room, just not any way to control the flow to the radiator)

UPDATE April 17th

I’m happy to report that these TP_Link HS100 smart plugs work perfectly (and directly) with OH2, so with a NodeRed Flow, I’ve mapped the Thermostat Heater channel state of a Velbus module.
(I could just of easily mapped this in DSL Rules, I just happen to be learning NodeRed right now)

Thanks to @Confused for putting this concept out there in the first place.
I’ve been going down all kinds of dead ends looking for an effective solution.