Vaillant Gas Boiler Pressure Issue: Drops to 0 in 2-3 Days, Adding Water & Air - 18yr Old Model

I warmly welcome. My problem is that the boiler does not hold pressure. For some time I have been observing that the pressure drops to 0 within 2-3 days. Initially, I was pumping air to 1 bar and for some time it was ok, after which it was falling towards 0, it was happening faster and faster. I started adding water trying to keep the 1 bar value. After warming up, the temperature remains in the range of 1, 5-1.7 bar. The problem is that despite adding water, the pressure keeps dropping. What happens with this air and water. If it goes down to 0 and I slightly unscrew the valve in the membrane, it hisses, so the air is, what about water, I add and add, and where is it. I do not observe leaks only once I heard the safety valve in the nobility for a moment. I mention that I have no idea about this boiler, I bought it together with the house, is already 18 years old, will anyone suggest something?

Buddy, if there are no visible defects, then from the safety valve. Check if it has an output connected to the duct

euterpi2 wrote:

I started adding water trying to keep the 1 bar value. After warming up, the temperature remains in the range of 1, 5-1.7 bar.

With the correct air pressure in the expansion vessel, the difference in boiler water pressure between a cold boiler and a heated one is usually around 0.2-0.3 bar.
From what you write, your pressure jumps by 0.5-0.7 bar, which suggests that you have too low air pressure in the diaphragm vessel and as a result of heating the water in the system, the pressure on the boiler increases, and if it exceeds 2.5 bar can trigger a safety valve and hence water loss. If the safety valve is connected directly to the sewer with a hose, you may not know that there was water dripping.

First of all, I suggest ruling out the problem of too low pressure in the diaphragmatic vessel.
The pressure is checked on an empty boiler after draining the water but with the drain valve open.
Its value should be 0.75 bar, although I personally pump to 0.9-1.0 bar and then fill the installation with water up to 1.4 bar according to the boiler pressure gauge. After heating the water, the boiler water pressure is 1.6-1.7 bar.

daro31ie wrote:

Buddy, if there are no visible defects, then from the safety valve. Check if it has an output connected to the duct

There is no drain to the sewage system. Maybe the water on the hot valve will evaporate and there is no trace?

euterpi2 wrote:

daro31ie wrote:

Buddy, if there are no visible defects, then from the safety valve. Check if it has an output connected to the duct

There is no drain to the sewage system. Maybe the water on the hot valve will evaporate and there is no trace?

Buddy, if not a drain, such a leak would be visible.
Do you have an open or closed installation?

BUCKS wrote:

euterpi2 wrote:

I started adding water trying to keep the 1 bar value. After warming up, the temperature remains in the range of 1, 5-1.7 bar.

With the correct air pressure in the expansion vessel, the difference in boiler water pressure between a cold boiler and a heated one is usually around 0.2-0.3 bar.
From what you write, your pressure jumps by 0.5-0.7 bar, which suggests that you have too low air pressure in the diaphragm vessel and as a result of heating the water in the system, the pressure on the boiler increases, and if it exceeds 2.5 bar can trigger a safety valve and hence water loss. If the safety valve is connected directly to the sewer with a hose, you may not know that there was water dripping.

First of all, I suggest ruling out the problem of too low pressure in the diaphragmatic vessel.
The pressure is checked on an empty boiler after draining the water but with the drain valve open.
Its value should be 0.75 bar, although I personally pump to 0.9-1.0 bar and then fill the installation with water up to 1.4 bar according to the boiler pressure gauge. After heating the water, the boiler water pressure is 1.6-1.7 bar.

Outflow to the sewer is not the question of what happens to water and air if the pressure flies to zero even when the boiler is not heating. What can be the consequences if I miss and turns on at a pressure of 0. What did you recommend to do after the heating season?

Added after 6 [minutes]:

daro31ie wrote:

euterpi2 wrote:

daro31ie wrote:

Buddy, if there are no visible defects, then from the safety valve. Check if it has an output connected to the duct

There is no drain to the sewage system. Maybe the water on the hot valve will evaporate and there is no trace?

Buddy, if not a drain, such a leak would be visible.
Do you have an open or closed installation?

I do not get twisted which means open and closed

euterpi2 wrote:

Outflow to the sewer is not the question what happens with water and air if the pressure flies to zero even when the boiler is not heating

Pressure drop means water loss. Maybe you have pipes under the plaster and the leak is hidden from your eyes.
Besides, you write that you do not know each other, you could have missed something.
It can upload a photo with a view of all the pipes coming to the boiler and give the exact, full symbol of your boiler. The model sticker is after opening the flap with electronics, when you see the circulating pump and the rest of the tubes in the middle of the boiler housing.

euterpi2 wrote:

What did you recommend to do after the heating season?

Since every few days you have a pressure drop to 0, I would check it now.
For this you need a car pressure gauge and a car pump and you can do it yourself, so you don't need a service technician but you can't have 2 left hands

I don't see much information here, what is in the pictures. I do not have documentation.

Symptoms may indicate a cracked / unsealed heat exchanger. Drips do not drip but during boiler operation more escapes and water simply evaporates and escapes with flue gas.

euterpi2 wrote:

I don't see much information here, what is in the pictures.

This is a vintage model, because I look at your photos like a calf on a painted gate

It looks like this is a 1-function boiler, because I cannot see the water inlet and outlet for hot water
It can be, as Gasak writes, that the primary exchanger is defective.
In this case, it is more likely to replace the boiler with a new condensing boiler, because the exchangers are expensive, in addition to such a monument there may be a problem with getting it, and from a demobil I would not risk it.
The sticker suggests that the last German review was in 1999 and we have 2018, so replacing the boiler with a new one is justified.
The new boiler means a modification of the connections, a modification of the chimney liner, so these are additional costs that you need to consider.

Thanks for the feedback, I have a second inheritance in the garage, maybe I will find the right master as a last resort. As for the chimney liner, it will probably not be a problem because straight from the boiler there is a copy and the outlet outside. Just tell me what the consequences can be, as at 0 the boiler will start

I do not know what this particular boiler is like, but in those I dealt with there was protection and prevented work at zero pressure.

Thanks for the help

gasak wrote:

but in those I dealt with there was security and prevented work at zero pressure

I have a Vaillant VUW from the 2-5 series, which is the model I associate with 2002-2004 but I know nothing about the safety device blocking the boiler operation in the absence of water pressure, so I doubt that the author's antique boiler should have such goodies. I will sooner believe this in new models with electronic pressure measurement.
If the circulation pump switches on in the absence of water then the pump can be bought. I don't know how the temperature sensors will react, but in theory you can burn the primary exchanger.
In total, I do not know, because I never turned on the boiler in the absence of water in the system, because I never automatically dropped the pressure to such a low level.

Thanks for the help

So don't take it for granted. The oldest boiler with protection I associate is Beretta from 1998, bifunctional. He was so mean / clever that after the heating season he switched to heating only domestic hot water at a pressure of 0 in the circuit which blocked.
Regards

This will be the western equivalent of Thermoblock. Single function with a single-row or newer three-row water-cooled T burner. The data plate will be on the flue at the front (the upper door must be opened). They had hydraulic safety devices - differential pressure required before and after the pump.

Yesterday I added water to the value of 1 bar I did not turn on the stove and overnight the pressure dropped by 0.2 bar, no traces of leakage can be seen

Added after 4 [minutes]:

This is the whole thing