PCB or communication fault: what to rule out before ordering a PCB

Short answer: a PCB or burner control unit for a boiler usually costs € 275 to € 460 as a part, plus fitting by an engineer. However, it is replaced far more often than necessary, because a communication fault looks exactly the same as a faulty PCB. First check the wiring, the connectors and the thermostat connection; in practice these are more often the cause than the PCB itself.

PCB, burner control unit and interface

Modern boilers contain several electronic components. The burner control unit monitors combustion: ignition, flame detection and gas valve. The main PCB controls the rest: pump, fan, sensors and communication with the thermostat. The user interface or control panel is the display you use for settings. On older appliances all of this is on one board; on newer ones they are separate modules that can be replaced individually. That saves money, provided you know which module it is.

The codes per brand

Brand	Code	Message
Remeha	11	Internal communication bus fault
Vaillant	F.11	No signal at the main PCB
Vaillant	F.12	No signal at the user interface
AWB	1.1	Communication fault
Bosch	1010 O	No communication via the EMS bus connection
Bosch	A8	CAN communication interrupted

Look carefully at the wording: almost all of these messages say "no signal" or "no communication". That is something different from "PCB faulty". A broken wire gives exactly the same message as a broken PCB.

What to rule out first

Start with the power supply: disconnect the boiler from the mains for thirty seconds and switch it back on. A PCB that has been confused by a voltage spike sometimes recovers this way. Remeha even has a separate message for this: a control fault due to a power interruption during writing.

Then check the thermostat wire. Two thin cores trapped somewhere behind a skirting board or gnawed by a mouse cause a communication fault that is reported as a PCB fault. To check, measure, or disconnect the thermostat and bridge the terminals (with on/off thermostats): if the boiler then fires, the problem is in the wire or the thermostat, not in the boiler.

Finally, look at the connectors on the PCB itself and at the wiring harness. Moisture, corrosion or a connector that has half vibrated loose is more common than people think. Vaillant reports a break in the wiring harness separately as F.25. All wiring can be found under cables and wiring harnesses.

What a PCB costs

Part	Manufacturer number	Price
Atlantic PCB with display	102215	€ 276.95
Weishaupt burner control unit W-FM	102012	€ 327.95
Itho Daalderop PCB including control panel	05-00234	€ 388.95
Panasonic PCB	ACXA73C40020	€ 459.95

All variants can be found under PCBs and controls en burner control units.

Watch the software version

This is the pitfall with PCBs. During the life of a series, manufacturers release new versions with different software and sometimes different connectors. A PCB from the same boiler series but a different year of manufacture may therefore not work or may first need to be parameterised. So always note the full type number and the year of manufacture of the appliance, and read the number on the old PCB itself. If in doubt, send us a photo of the PCB and the rating plate before you order.

With some brands a new PCB has to be set to the correct boiler type and output after fitting. This is done with a service tool or via a code sequence; leave that to the engineer.

Repair or replace?

There are companies that refurbish PCBs, and for older appliances for which a new PCB is no longer available, that can be a solution. For current series a new PCB is usually the wiser choice: you get a warranty and the latest software version. For a boiler over twelve years old, it is worth weighing the cost of PCB plus labour against a new appliance.

Frequently asked questions

How much does a PCB for a boiler cost?

The part usually costs € 275 to € 460, depending on brand and type; on top of that comes fitting by an engineer and, with some brands, setting the new PCB to the boiler type and output. For a boiler older than twelve years it is sensible to set that bill against the price of a new appliance.

My boiler does nothing at all any more. Is the PCB broken?

First check the power: plug, fuse and RCD. A dead display is more often due to a tripped circuit or a faulty transformer than to the main PCB itself.

Can I replace a PCB myself?

Electrically it is straightforward work, but you are dealing with the controls of a gas appliance and the PCB often has to be set up afterwards. Moreover, it is work that should be done by a certified gas engineer. You can order the part yourself; have it fitted by a professional.

Why do so many boilers report "no communication"?

Because modern boilers talk to the thermostat via a bus connection, such as OpenTherm or EMS. If that connection drops out, the boiler no longer knows what is being requested and reports it. In nine out of ten cases the cause is the wire or the thermostat, not the boiler.

Does a reset help with a PCB fault?

A reset clears the fault, but not the cause. If the same message comes back, have it measured instead of resetting again.