They are not talking

During the previous winters, I noticed that my natural gas boiler would start heating and stop after a few seconds for no apparent reason. It was something I noticed because I had not been using any hot water and the room temperature were very high in all rooms.

There are 3 reasons for it to start heating water. 1 the circulating water in the floor for heating are getting too cold and needs to be warmed up. 2 the hot water for the taps need to be heated. 3 the legionella protection (also called anti-legionella function) kicks in and heats the water when the temperature for tap water has not been above 60°c for a week. 

The heating system for the house are entirely based on the heating pipes in the floor, one loop for (almost) each room. (with my surplus electricity from my solar power installation, I also have a aircon / heat pump I can use, but that is secondary heating source). The thermostat in each room measures the temperature and the controller shuts off water when it isn’t needed in a room. So when all rooms are shut off, there are no need for heating and pumping the water. 

The problem is that the boiler does not know that no warm water is needed for heating, so it keeps pumping and trying to keep the temperature of the water at 25°- 35°c (depending on the temperature outside) even when all valves are closed. 

So late one evening last fall, I dug out the manuals for the boiler and the control system for the floor heating. I had glanced over them a few times before and I got the impression that it should be possible to tell the boiler not to heat or pump water 24/7 but only when it was needed.

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The box controlling the floor heating

The paper I found inside the controller unit of the heating system, shows a relay that should be able to switch power on and off to a pump. It is not a control current but a relay for 220v.

Paper found inside along with another paper explaining that some sort of test had been done on the entire system after installation and they had also been nice enough to leave a paper explaining which color wire went to which room. Thank you.

So the first thing I did was to see if it worked as advertised and I checked it with my multimeter. Tried to turn up and down the heat, but it didn’t seem to work. Then I found a flashlight and took a look at the relay and discovered that I had been looking at the socket for the relay. Stupid me.

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Inside the box

Googling for this controller revealed that it had gone out of production and the relay was an optional extra which was impossible to find except one webshop in the UK which may or may not have had it in their inventory and if they did, it was way too expensive. But the socket for the relay seemed fairly standard so I looked for the data sheet for the socket to get the right dimensions for the relay. If I remember correctly, there are two types of relays with almost identical space between the connectors except for a millimeter or two.

Anyway I found the nearest online electronics store and purchased 2 relays. One for each size. There are different types for different usage and amps but it doesn’t matter for this use, I just need it for a control current. So nothing to do than go to bed continue when the relay arrives. 

A few days later the relays arrived and I could continue my test.

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The relay

The manual for the boiler shows 3 separate rows of connectors and on one of them it should be able to connect a relay or a switch or thermostat to tell it if I should run the pump and heat water for keeping the house warm.

When I opened up the boiler it only had 2 rows of connectors, but fortunately one of them had the desired function and there was a sticker explaining it. 

Some of the text on the sticker reads: “To fit a room thermostat connect it to terminals 1-2 after removal of the link between them” and “DO NOT FIT A ROOM THERMOSTAT EQUIPPED WITH A RESISTANCE RELEASING IN ADVANCE”.   

So it seems is exactly what I was looking for. I have a relay in the control box that behaves like an on/off thermostat and not resistance based.

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One of the connectors in the boilers.

I connected the relay to connector 1 and 2 and it worked perfectly together.

When all the thermostats shuts off, the controller tells the boiler it doesn’t need more heat so if it is running it stops heating.  2 minutes after the boiler has bee running last time, it shuts off the pump, so if it hasn’t been heating for some time, it shuts of the pump at once. after 3-4 minutes(I think) the controller shuts off the valve(s). 

Now it has been running last winter in this configuration and from my casual observation it seems that the pump now only runs 1/3 of the time and I have no more of those false startups where it wastes gas heating for nothing.

I wish they had made that connection when they installed it. It was very cheap in parts and it has paid for itself in a year in electricity savings alone. The boiler uses slightly less natural gas now and less wear because it does not start so often.

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