Repair of the Ariston Boiler Control Unit with error 104 - Insufficient circulation

Hello dear visitors of this site!

Once my gas by-pass boiler Ariston Clas 24 FF, again demanded urgent, surgical intervention. The reason for this was his following behavior.

The boiler, being in heating mode, turns on, ignites and after a few seconds, making eerie sounds of rapidly boiling water in the heat exchanger with some kind of mechanical click, turns off and goes into emergency mode with error code 104.

Insufficient circulation, error 104. How I looked for the cause

According to the manual, I determined that 104 is "Insufficient circulation" I argue: What can interfere with normal circulation? After all, a clogged filter in the heating system or slag that has accumulated in the primary heat exchanger can interfere with the desired flow of the coolant. Or maybe the reason is in the circulation pump? Did the pump really fly? To check it, unscrew the drain screw on it, this will allow you to see whether the shaft rotates or not.

This must be done carefully, as water may start to come out, not much, but it is better to put some kind of rag so that it does not fall on the board.

There is a slot on the shaft for a wide, flat screwdriver, I tried to turn the shaft with a screwdriver ... it did not jam, it rotates. I try to start the boiler and see if the shaft rotates. The cauldron reproduces its terrible sounds and again goes into defense. The shaft does not rotate. At the time of launch, I tried to turn it with a screwdriver…. I thought, and suddenly there was a "blind spot" ... .. no, the rotation of the shaft did not follow.

I decided to check the pump supply voltage. When the presence of 220 volts was found on the chip, the conclusion was unambiguous…. Replacement pump. Eeeh I think, again, unforeseen expenses.

However, the conclusion was hasty, when I was looking for wires going from the board to the motor of the circulation pump, I noticed that there were more than two of them. For what? I started to figure it out and that's what I found out.

Why Error 104 - Insufficient Circulation Can Occur. Eliminating the malfunction

The circulation pump of the boiler has two rotation speeds in the manual, they are designated as V2 (55 W) and V3 (80 W). The ECU naturally controls the pump speed.

In hot water (DHW) mode, the pump runs at V3 speed for better heat transfer.

In central heating (CH) mode, the control unit switches the pump speed depending on the temperature difference between the inlet and outlet of the heating system.

Therefore, the pump is controlled not by one, but by two relays. One supplies 220V power, and the other controls the speed.

To check these power circuits, the pump will have to be turned on. But for this you do not need to light the boiler, we do not want to rape him. There is an item in the control menu that allows you to do this, but you have to deal with the menu.

I used a different, faster way. It is necessary to switch the boiler to the “Blowing” mode. To do this, press the ESC button on the boiler panel and hold it pressed for more than 5 seconds. The purge mode is activated - this is a mode in order to remove air from the heat exchanger and the circuit. It turns on for 6 minutes, or you can turn it off forcibly by pressing ESC again. During the operation of this mode, the circulation pump starts and runs in cycles of 60 seconds. incl. 30 sec off and so on for 6 minutes. and without igniting the burner. And that's what we need!

So we start the "Blowdown" mode and measure the alternating voltage at the terminals. We look at the drawing.

In my case, it was so, from the RL 04 relay, 220 volts were supplied to pins 3 and 4. but the pump did not rotate.

The contacts of the RL03 relay (pump speed control, relay type JQX 118F), when the boiler was turned off with a multimeter, rang shortly, which is the norm for a lower rotation speed, but under load the relay behaved incomprehensibly as the pump motor did not turn at all. As soon as the pins 5 and 6 were closed with tweezers, the pump began to work. Output faulty relay control pump speed.

Therefore, until the time until I select the relay for replacement, I simply soldered the jumper i.e. bridged 5 and 6 pins from the mounting side. In fact, a serviceable relay performs almost the same work, closes this circuit or switches it to another contact, this is how the pump speed switches. By closing the contacts, low speed is turned on.

Layout of the relay on the board.

Photo of the board with a jumper, and explanations for the pump speed control relay.

According to the repair manual, error codes associated with circulation are codes 103 —104 —105 —106 —107.

But remember insufficient circulation can be not only due to a relay or pump, do not dismiss the filter in the heating circuit, filter or heat exchanger, they can be clogged and also interfere with normal circulation.