# Central heating system extension

#### Swartzy

Joined Dec 24, 2020
16
Dear Forumers,

I would like to ask for your help in solving the below task (it will be an extension of the current central heating system of mine). What do you think what is the easiest way for it?

If 1&2 wires are closed but 5&6 are not 1’&2’ should be closed

If 3&4 wires are closed but 5&6 are not 3’&4’ should be closed

If 5&6 wires close 5’&6’ wires should be closed but 1’&2’ nor 3’&4’ should not be closed until 5&6 are closed

1&2 and 3&4 operates independently.

Thank you.

Sincerely, Swartzy

#### sghioto

Joined Dec 31, 2017
1,801
OK a truth table.
Line 3 appears incorrect. I think you mean anytime 5,&6 are closed then 1&2 and 3&4 will have no effect until 5&6 are open?

#### Swartzy

Joined Dec 24, 2020
16
OK a truth table.
Line 3 appears incorrect. I think you mean anytime 5,&6 are closed then 1&2 and 3&4 will have no effect until 5&6 are open?
Yes I mean exactly that.
What would you use for this project? Raspberry or Arduino with relay shields?

#### MisterBill2

Joined Jan 23, 2018
7,697
The TS has chosen an interesting way to ask a question and it is not how heating system controls are usually represented. In fact it is not clear how the post relates to "an extension" of a heating system at all.
So is the TS seeking a way to connect an additional thermostatic control or just exactly what is the desired extended control??

#### ElectricSpidey

Joined Dec 2, 2017
1,397
Is this a 240 volt system where "1 & 2" are switching both hots to a single set of heaters?

Or is "1 & 2" switching two 120/220 volt heaters?

Are the combinations listed always closed/open together? IE: "1 & 2"

Are these control switches or direct load switching?

More info is needed, but it sounds like a job for properly rated relay/s.

#### sghioto

Joined Dec 31, 2017
1,801
What would you use for this project? Raspberry or Arduino with relay shields?
It would depend on what is determining when the "terminals" need to open and close. Assuming one or more thermostats?
Can you provide a block diagram of how you want to expand the system.

#### MisterBill2

Joined Jan 23, 2018
7,697
First, toy computers have no place in anything as critical as a heating system.
Next, what sort of heating system is this? the scheme does not match any system that I have worked with? And it seems perhaps that the TS is asking about expansion of a system to include more areas. But without more understanding of what is in place already there is no way to make a sensiable suggestion as to what should be added.

#### Swartzy

Joined Dec 24, 2020
16
We have this zone controller:

My goal is if Z3 active, disable Z1 and Z2 zones until Z3 becomes inactive. This is a Computherm Q4Z Zone controller. I have not found a diagram of the circuit.

#### MisterBill2

Joined Jan 23, 2018
7,697
After seeing the picture of the controller board and seeing that there is a control tagged "boiler" now I understand that this is a zone controller for a hot water heating system. So my question now is about the devices that this unit controls. I am familiar with systems that have a thermostat for each zone, and a valve for each zone, and a single circulation pump that becomes active when any zone demands heat. So the diagram needed is what connects to these terminals, not what is inside this board. But with multiple sets of terminals tagged with zone numbers it becomes confusing. And where are the thermostat connections?
In addition, there is probably a lot more to this system than is shown.
Is there a manual that describes the functionality of the different outputs?
I see three sets of blue terminals that may become active when different zones are enabled. If that is the case then it may be possible to do some external relay logic to have some zone exclusion functionality.

One additional observation is that each group appears to be a complete power output, line, neutral, and ground, so that they are not individual contacts but each a whole output.
And my guess is that there are separate sources of heat that the TS wants to enable depending on which zones are demanding heating.

So just a simple block diagram may provide a basis for understanding the desired functionality.
Thisis not a case of being able to provide a useful answer when we are given only a tiny bit of information.

#### Swartzy

Joined Dec 24, 2020
16
I would not like to mislead anyone with a block diagram what I create (lack of skills creating one) let me describe what does the above board do. I also have no english language manual for the board only this hungarian - http://ketkorkft.hu/_userfiles/ketkor/file/Computherm/Q4Z_2013_HUN.pdf

The thermostats connects to the connectors T1-T4 respectively.
Slow opening & closing electrothermic valves for the zones connects to Z1-Z4 respectively.
In my case there are two valves and an underfloor heating circulation pump connected to Z2.
BOILER output is an output with "no potential" what controls the heater ("no potential" is according to the manual but I don't really know what does it mean. My guess that 240 VAC power is not presented on BOILER output, it just only a simple relay. In my case the main circulation pump is controlled by the heater not by the zone controller board).

Working of the above board:

When T1 closes Z1 output becomes active meaning 240 VAC presented on Z1 until T1 remain closed. When T1 thermostat opens Z1 power output stops.
Same story to:
T2 -> Z2
T3 -> Z3
T4 -> Z4
The thermostats and the Zone outputs works independently from each other.

The blue connectors:
Z1-Z2 is active if any of T1 or T2 thermostats are active
Z3-Z4 is active if any of T3 or T4 are active
Z1-Z4 is active (in my case its delayed see below) if any of T1-T4 are active
BOILER output is active (no power output is present) if any of T1-T4 are active
There is a DELAY jumper set to ON on the board. When any of T1-T4 inputs close the BOILER and the Z1-Z4 output not immediately becomes active, just only 4 minutes later. Its because the zone valves are slow opening types and the main circulation pump may become damaged in working while the valves are still closed.

My goal:
Priorising Zone 3. When Z3 is active turn off the other zones.
Altering the inputs or outputs also possible but what do you think what is the easiest way for it?

Thank you Guys

#### MisterBill2

Joined Jan 23, 2018
7,697
The very simplest way would require one relay with a mains voltage coil, 220 volts, and two sets of normally closed contacts. The normally closed contacts would be in series with the line connections from the Z-1 and Z-2 terminals. Probably the relay will have contacts in a 3 terminal (form "C" arrangement), which is fairly common.
The benefit of this scheme is that it makes no change to the controller and it is simple to change back if the results are not satisfactory. In addition it is probably the least expensive approach that does not require making changes in the controller circuit board.
The same scheme could also be used to open the thermostat side connections instead of the zone valve connections, which could use a smaller relay.
If the relays K1 thrugh K7 include an unused normally closed contact then there would exist a possibility of a change to the circuit board arrangement without adding an external relay. But that would be complicated, and would require cutting traces on the circuit board and adding jumper wires.

#### DanSohan

Joined Jan 6, 2021
18
First, toy computers have no place in anything as critical as a heating system.
Next, what sort of heating system is this? the scheme does not match any system that I have worked with? And it seems perhaps that the TS is asking about expansion of a system to include more areas. But without more understanding of what is in place already there is no way to make a sensiable suggestion as to what should be added.

That's an interesting comment as a large number of commercial units I've serviced (laser cutters, CNC machines, plasma cutters and industrial robots) have the exact same uC as the Arduino... Some even have the actual Arduino inside! Seems okay for heavy industry, seems fine to use at home for me. As long as the correct isolations are used and installed by someone adhering to local laws, and the coding is sound... What would class a computer as a "toy computer"? The hardware itself of the user / developer of said device.

(I use an Arduino in my own central heating system with confidence)

#### MisterBill2

Joined Jan 23, 2018
7,697
Upon reading more of what the TS is asking about there is no application for additional computing power. Andan arduino does not have the I/O hardware to fit the situation. Even better, the functionality requested can be provided by a single 2 pole relay. Contact closing inputs and 220 volt outputs is not arduino's realm,at least not without a bunch of add-on parts

And the fact that the same processor is used in a better device does not impute ruggedness or capability to another device.

Once the actual application was explained the solution became fairly clear to me.

#### Swartzy

Joined Dec 24, 2020
16
The very simplest way would require one relay with a mains voltage coil, 220 volts, and two sets of normally closed contacts. The normally closed contacts would be in series with the line connections from the Z-1 and Z-2 terminals. Probably the relay will have contacts in a 3 terminal (form "C" arrangement), which is fairly common.
The benefit of this scheme is that it makes no change to the controller and it is simple to change back if the results are not satisfactory. In addition it is probably the least expensive approach that does not require making changes in the controller circuit board.
The same scheme could also be used to open the thermostat side connections instead of the zone valve connections, which could use a smaller relay.
If the relays K1 thrugh K7 include an unused normally closed contact then there would exist a possibility of a change to the circuit board arrangement without adding an external relay. But that would be complicated, and would require cutting traces on the circuit board and adding jumper wires.
Dear MisterBill2,
Thank you for your great post! I understand the situation and I could do it on the Z side but
how can I carry out the project from the thermostat side? What type of relay do I need? A simple 3V relay with two NC terminals would work? (like this one https://eu.mouser.com/ProductDetail...GAEpiMZZMtGt%2Bn33CgIP0LOEstN9G3HPOo3ObaOEEQ= ) I suppose no external power is needed for the relay, is it?
Thank you
I measured the voltage between the two poles of the T3 connectors.
When thermostat is not closed (causing zone 3 to be inactive) 2.9 volts measured.

When thermostat is closed (causing zone 3 to be active) 0 volts measured.

Additionally I measured the voltage between the T3 and the ground.
Inactive situation:

Active situation:

Last edited:

#### djsfantasi

Joined Apr 11, 2010
7,210
i agree with you here.

And an arduino does not have the I/O hardware to fit the situation. <omitted> Contact closing inputs and 220 volt outputs is not arduino's realm,at least not without a bunch of add-on parts[
Your follow-on statements may not be supportable. Have you ever used Arduinos in several different projects? It’s I/O hardware is fairly robust.
• 54 Digital I/O pins
• 15 PWM output pins
• 16 Input Analog pins
Admittedly, additional hardware may be necessary to interface low voltage low current output to external devices. But so do other solutions.

The advantage to using an MCU is that operational logic is easily implemented with programming skills. And doesn’t require a bunch of add-on parts to implement the logic.

I’ve used an Arduino Mega to control six RC servo motors, two 1A hobby motors, play pre-recorded sounds and close to 100 LEDs. It has sufficient I/O capabilities for me and I can control all such devices with just a few modules (shields) and determine patterns of operation in code. And change the behavior on a whim.

I’ve written a proprietary language that is stored on an SD card to control 11 RC servos, play pre-recorded sounds, scan a room for occupants, and collaborate with other systems on a network. These will be used in a production environment. And I can change behaviors on a whim. The Arduino allowed quick development of these devices.

Again, I’m not disagreeing with your basic point, but arguing with your supporting statements. Arduinos are not always appropriate. Nor are they a toy.

#### sghioto

Joined Dec 31, 2017
1,801
how can I carry out the project from the thermostat side?
Same as before but contacts wired to T1 and T2.

#### MisterBill2

Joined Jan 23, 2018
7,697
Originally I suggested a 220 volt coil relay for the reason that connecting it to an AC output that had the desired operation would be very safe in avoiding any chance of damaging any part of the thing. AC power controlling AC power with the connections very well defined is a simple and safe approach. Another option would be a 12 volt relay powered by connection to the coil of the relay that operates the Z1-2 output. That would require making solder connections to some fairly small solder pads on the board, and not ever person who posts can solder well.

The circuit in post #16 will work very well.

#### MisterBill2

Joined Jan 23, 2018
7,697
Yes, it seems that if there is a way to use the T3 thermostat closing to provide a 12 volt signal to a small relay then tha relay can open the connections of the thermostats for zones 1 and 2. And working with a lower voltage and a much lower current makes the effort safer. Very good thinking!!

#### MisterBill2

Joined Jan 23, 2018
7,697
i agree with you here.

Your follow-on statements may not be supportable. Have you ever used Arduinos in several different projects? It’s I/O hardware is fairly robust.
• 54 Digital I/O pins
• 15 PWM output pins
• 16 Input Analog pins
Admittedly, additional hardware may be necessary to interface low voltage low current output to external devices. But so do other solutions.

The advantage to using an MCU is that operational logic is easily implemented with programming skills. And doesn’t require a bunch of add-on parts to implement the logic.

I’ve used an Arduino Mega to control six RC servo motors, two 1A hobby motors, play pre-recorded sounds and close to 100 LEDs. It has sufficient I/O capabilities for me and I can control all such devices with just a few modules (shields) and determine patterns of operation in code. And change the behavior on a whim.

I’ve written a proprietary language that is stored on an SD card to control 11 RC servos, play pre-recorded sounds, scan a room for occupants, and collaborate with other systems on a network. These will be used in a production environment. And I can change behaviors on a whim. The Arduino allowed quick development of these devices.

Again, I’m not disagreeing with your basic point, but arguing with your supporting statements. Arduinos are not always appropriate. Nor are they a toy.
Every one of those digital I/Os is a pin on a connector at a very low voltage and current. So none of it is able to do any serious controlling without a whole lot of additional hardware. And external powersupply, and terminals and an enclosure to protect it from everything and avoid short circuits because of touching something. And that includes the low powered PWM outputs.