Gas boilers operate in a closed system and have a 3bar safety valve, which, according to the standard, can fire already at 2.5bar, but certainly must fire after exceeding 3 bar, and the photo shows 3.6 bar, so something is wrong with the protection.
If the safety valve is connected directly to the sewer then under normal conditions you may not even notice that it has tripped. Some boilers do not have the safety valve connected to the sewer, so if the valve is tripped, water will gush onto the floor and flood the boiler room then you can see, that it tripped
Drututu wrote: I do not have a manual for the furnace
Write down the exact symbol of your boiler and download the manual from the net from the manufacturer's website.
Unusually the pressure of cold water on the boiler is in the range of 1-1.5 bar, with an efficient boiler after heating the water pressure jumps by about 0.2-0.3 bar, that is, in practice with an efficient boiler will never exceed 2 bar.
To maintain a safe pressure level is responsible in the boiler diaphragm vessel, which if it has not been controlled and has a loss of air will cause pressure spikes.
Also, in addition to checking the valve that allows cold water into the central heating system, I would check the diaphragm vessel to see if it has the correct air pressure.
Typically, manufacturers state that the vessel should have 0.75 bar.
I in my vessel adopted as the maximum air pressure of 1.0 bar, then on a cold boiler I pour water to a pressure of 1.4 bar and after heating the water in the system to 60 degrees, the pressure jumps to a level of approx. 1.60-1.65 bar.
The apparent 3.6 bar is an obvious error and it can not be like this all the time, because it threatens to damage the central heating system as well as the boiler.
Unless the pressure gauge on the boiler is going crazy and shows wrong data.
I personally would first check the diaphragm vessel, because it most often causes problems. There should be somewhere in the boiler near the wall such a flat rectangular or round one colored, for example, red. In my boiler, the valve from the diaphragm vessel was on top near the flue pipe, meaning I needed a ladder to check the air pressure in the vessel.
The diaphragm vessel has a valve identical to those in car wheels, so the problem with the vessel can be different:
- the pressure in the vessel has dropped due to the lack of periodic, annual inspection and possible refilling of the pressure, analogous to the way it can be in car or bicycle wheels where the air over time spontaneously escapes below the recommended level. Simply inflate the vessel with a car pump to the recommended level, after draining the water from the boiler and with the drain valve open.
- in the vessel, the valve that lets air through has been damaged, so you need to replace it with a new one and refill the air pressure as above. As a precautionary measure, when checking the pressure, you can replace the valve with a new one, so that later you do not drain a second time if the valve is actually damaged.
- the diaphragm in the vessel has been damaged and the entire diaphragm vessel is to be replaced.
As you rule out damage to the vessel or lack of air in the vessel, you can look further and see if the valve that fills central heating with tap water is operational and closes the circuit.
Sometimes in 2-function boilers the problem can be generated by the plate heat exchanger from the heating of hot water, which, if it has internal perforations, can be the place where tap water pours into the c.o., and in the case of a lack of tap water pressure, it can cause "contaminated" central heating water to spill into the potable tap water system.
Either determine what's wrong yourself, or if you think it's beyond you, call a service technician, because 3.6 bar is a condition that requires immediate attention.
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