Help with host

so guys i have a connected thermostat that asks me for a Mac and Host IP , in the host section should i put the thermostat IP or router IP?

Assuming you’re configuring the thermostat itself, what does the manual for the thermostat say?

There’s no way for anybody to answer such a vague question. You’ve done the equivalent of phoning your garage and saying why won’t my car start. See this sticky post and then edit your question to include actual information.

The thermostat is asking for this information? Seems you should follow the thermostat’s setup instructions.

Why would you put in the router IP? That doesn’t seem to make any sense.

well problem is that it doesnt say if it is the router or the thermostat IP but im confused about the host

WHAT is IT? WHAT doesn’t say something?

If you are referring to the configuration of the component, I ask again, Why would you put in the router IP? What does the router have to do with ANY of it?

If you are referring to something else, you will have to explain

The thermostat is going on your local lan and not everybody has a DHCP server (on the router generally) that can fix ip address’s (that’s why I binned my last one) so sometimes the only place you can do it is on the kit itself. So set a 'fixed IP address for this new vital bit of your kit.
The router it will pick up when it boots as it can’t talk to anything else without doing that especially as the router is also the gateway and your modem.
Host - Not a clue - maybe this kit is part of a system that they sell and their ‘host’ also then talks to a boiler and A/C package to help you control the temperature
Just a guess

Having Re-read the whole thread, let’s start again.
What is the kit you have bought?
Do they also supply a control station or something similar?
Do they have a boiler interface device?
Do they have anciliary temperature sensors? Or do you just add more thermostats?
Who recommended this kit to you? Friend? Supplier? Smart home automation vendor? Or bought from an ad?
Do you have a link to any information on line?
Preferably English, as I can’t read Greek
If they have a ‘system’ then they ‘should’ auto discover each other, so not inspired by your manual so far.
Information is your friend, ignorance your enemy

well here is the link and the component configuration yaml that says for the host is this :

  - platform: hysen
        name: Main Thermostat
        host: 192.168.X.X
        mac: "XX:XX:XX:XX:XX:XX"
        name: Secondary Thermostat
        mac: "YY:YY:YY:YY:YY:YY"

if you see that Id like to ask something else also in the first step it suggests to keep host IP empty in order to make it summon the Wifi Services properly though it gives me errors in the homeassistant when i do that , is that possible to be done without errors? it says in the errors log that host cant be empty

Okay, we’re cooking on gas …
The host here is your thermostat that you are setiing up.
Can you set fixed IP addresses on your router ?
Set your thermostat up assign it an address and then put that address and it’s mac in under Main Thermostat, If you have another put that under … “yes you guessed it … secondary thermostat”
I have 49 slots from to available for random stuff on my network I like to keep the rest of the range for infrastructure so assuming you are on the same Class C range then set your host to something in that range. You may have a different stategy.
IP address and mac can be found by either looking at clients from your router or using any standard IP Scanner program.
Yes there are two steps here which you have assumed go together.
1a. Put your thermostat on the network
1b. Assign it a fixed IP address according to your infrastructure strategy, don’t let it wander or HA won’t find it again, if you upgrade firmware or have a power outage or …
2. type the results from 1 into HA config

NOTE : At the moment, you may have to setup the device Wifi connection with the horrible “Room Heat” app, that was supplied with the device. In test, if you setup the above with no IP and valid mac, e.g. 30:30:30:30:30:30 the service will fail to load the device, but will setup services that can be called to enable you to setup the device wifi properly.

If you actually left a line that says host: and didn’t have anything there, then delete the line.

In answer to your question, you have to tell home assistant the IP address of the device you want it to control. If you gave your router IP it wouldn’t do anything at all. It’s not using the router to control the thermostat.

Host means a device on the network. It may be a computer, a tablet, an esp device, a hub, whatever. They are all computters with an IP stack.

A host is referred to by IP address, but they are confusing and hard to remember, so way back in the dark ages they invented DNS. It converts a hostname to an IP address.

TL;DR put the ip address (or hostname if DNS works on your LAN) of the thermostat.