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Samsung heat pump - data cable issue

Steveimpey · 2026-07-15T11:04:45Z

My heat pump journey has never been smooth (I've had two installed at two different properties) My latest issue is with my 12 kW Samsung EHS Mono Gen 6. It was installed 3 years ago and up until a few days ago it ran well until I lost hot water and started getting two error codes E101 and E604, which apparently relate to data transfer between the heat pump and controller. Having spoken to Samsung, their first question was to ask about the cable that runs from the F1 and F2 terminals. Upon my electrician checking it appears 4 core cat 6 data cable was used instead of the the 2 core shielded CY data cable specified by Samsung. This has lead to the communication chip on the PCB having to work much harder due to "noise" which has resulted in it's failure. Just to say, it wasn't a BUS install and the installer isn't MCS. accredited. (Installed in new build). I'm on good terms with the heating engineer who installed it and I don't want to damage our relationship, However, I'm now going to end up out of pocket due a new PCB being required along with running a new shielded data cable for a problem that should not have arisen in the first place. I'd love to know other forum members experience of the data cable issue. Is this a wide spread problem? As an "end consumer" I don't expect to have to know about this, I just expect a fully functional reliable product.

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Air Source Heat Pumps (ASHPs)

Last Post by bobflux 13 minutes ago

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Majordennisbloodnok

(@majordennisbloodnok)

Famed Member Moderator

Joined: 5 years ago

Posts: 1992

18/07/2026 12:21 pm

Posted by: @jamespa

↑

Posted by: @majordennisbloodnok

↑

A resistor won’t clear up noise.

Is that the case? Surely the terminating resistor also reduces the impedance of the circuit, and thus induced currents will generate smaller voltages

You may well be right; I am by no means an expert. It’s my understanding, but I am happy to be proven wrong. I’d welcome any electronics experts to wade in at this point.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and SPH5000 inverter
1 x Myenergi Zappi
1 x VW ID3
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; sumus solum profundum variat"

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bobflux

(@bobflux)

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Joined: 5 months ago

Posts: 130

18/07/2026 2:20 pm

If it is RS485 (is it?)...

It uses balanced/differential twisted pair link. The idea is to send the signal on one wire, and the inverted signal on the other wire. For example, one wire +5V the other 0V to send "1", and one wire 0V the other +5V to send "0".

Voltage between both wires is called "differential mode" and is your actual signal. Voltage between the average of both wires and receiver ground is called "common mode". In the above example, differential mode is either +5V for "1" or -5V for "0" and common mode is 2.5V.

The idea behind balanced differential transmission is:

1) The receiver compares (or subtracts) voltages on both wires to decode what was transmitted. It does so while doing its best to ignore common mode: shifting both wires' voltage by the same amount doesn't change the result.

2) We want both wires to receive noise in the exact same way, ie common mode, so the receiver can reject it. For this, the wires should have the same impedance, and they should be twisted.

Two parallel wires in a perpendicular electric field receive a noise voltage between them. Twisting the wires cancels that, and also makes more of the noise common mode.

In a variable magnetic field, induced current in a wire loop is proportional to loop area. Area between the wires is tiny, so for all intents and purposes, there is almost no induced current in the loop formed by the two wires. However, the cable is long, and it forms a very large loop with the other return wire, which is Protection Earth. Therefore, induced current problems are mostly common mode, within the loop Device1 - comms cable - Device2 - Earth - Device1. The solution to this is to use isolated RS485 transmitters to break the loop (this is very common), and connect the cable shield at both ends to ensure both RS485 chips have a common ground and don't see harmful common mode voltages. Ironically this is almost never done, all you get is two terminals "A" and "B" and nothing to connect the shield, which makes the shield mostly useless.

The termination resistor is to avoid signal reflections in the transmission line, which only cause problems if the rise time of the signal is quicker than propagation time in the transmission line. This is not usually an issue at the low baud rates used in these links.

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