Vaillant ecoTec plus 186/3-5 Dropping water pressure, water escaping from the stove

Hello, for several months I have been topping up the amount of water in the system more and more often, and for the last few days I have had to do it every day. Error F22 appears, the pressure indicator shows too low pressure (0.3-0.5). Just add water and the stove starts working, clearing the error.
The installation is tight. The only thing that caught my attention was water leaking at the bottom of the stove from the marked hole.



Does anyone know what the problem is?

This one is just that.
There is a leak in the tank or fittings.
You have to look deeper, because it is mainly the nameplate that is marked.
And the leak seems hidden. Good luck,.

This topic has been discussed on the electrode several times.
What is leaking is from the safety valve. In CO it is 3 bars.
When you add water to the central heating, the water heats up, increases its volume and the pressure increases. Yours is above the permissible 3 bars. The most common cause is a problem with the expansion vessel, which should take over the increase in water volume after heating and stabilize the pressure. Either the vessel is damaged or air has escaped from the gas cushion.
It is best to check this by pressing the valve in the expansion vessel. The vessel is accessible after removing the front cover from the boiler. If water comes out of it, it means that the vessel is damaged. If the air flows weakly, it means that the air bag is too small. But in order to "create" the appropriate pressure in the vessel, you need to close the shut-off valves under the boiler - these are the valves under the boiler on the left and right side of the boiler, closed with a flat screwdriver or a 4 mm Allen key, then drain the excess water and pressure from the boiler using the drain valve (one of the side valves (square shut-off valves with an 8 mm open-end wrench) and with the open drain valve, increase the pressure in the vessel to approx. 0.9-1.0 bar and wait a while and check whether the pressure is maintained. If it persists, turn off the drain valve, open the central heating shut-off valves and let water into the central heating up to a pressure of 1.2-1.5 bar.
Important note - turn off the gas in advance so that the boiler does not start the burner in an unvented boiler. Either you need to run the P.00 program to vent the boiler several times or let it try to turn it on with the gas turned off - however, after several unsuccessful ignition attempts, the boiler will throw error F.28 or F.29 - you need to delete this error and let the boiler try to start again. The idea is to vent the boiler sufficiently until you can no longer hear the water and air flowing through the boiler, only the quiet flow of the water itself through the boiler.

Gentlemen, what if the system is tight, only air comes from the valve, and you have to top it up every few days because the pressure drops.
I would like to point out that I have about 450 L of water in the system, steel and copper pipes, mostly cast iron radiators and a few smaller ones (aluminum or something).
Furnace: ecoTEC Plus Vaillant VC 306/5-5, power at 6.4-31.8 kW, max. power when heating domestic hot water 34.0 kW;

the vessel must be of appropriate capacity adapted to the capacity of the boiler water supply. Without calculations, it is simplified to assume that you need an expansion vessel with a capacity of 1/10 of the tank capacity. So if you have 450 l, you need a vessel of approximately 45 l. The vessel built into the boiler is usually 6-10 l, so you need to have a second, additional vessel. The pressure in the vessel should be appropriate, depending on the static pressure of the installation, so sometimes it must be much higher than the typical 0.75 bar in a gas boiler vessel.

As my colleague BUCKS already wrote, there should be an additional vessel.

Take photos of the connections under the boiler, because you may have a sewered drain from the safety valve and no water flow is visible.

Hello,
Buddy, don't force open doors!
Buy an 18-24 liter expansion vessel with a band or beam for PLN 200, inflate it to 1.2 bar (i.e. with a small reserve for air escape, plug it in wherever suits you and that's it (check the above-mentioned pressure once a year) .
Greetings

Ok, that's what I thought and that's what I'll do. Thank you very much.
However, maybe I will add it as a curiosity and I will ask why this also happens in the summer when there is no heating (I do not close any valves, only the room sensor does not heat), but only domestic hot water is heated?
A 2-function furnace with a boiler and this hot water system has a diaphragm function.
I'll post a photo in the afternoon