[Solved] Vaillant Dual-Purpose Gas Furnace: Low Pressure Issues, S54 Code & Expansion Tank Queries

Hello! I have a problem with the low pressure in the gas oven. Slightly above zero it is only when the stove is turned off, when it fires up, the pressure rises to 1 and remains there. If I raise the pressure before turning on the stove to 1.6 bar, it will stay there as long as the stove is running. When it is turned off, for example at 10.00 pm, at 5.00 am, the pressure is slightly above 0 or 0. It's strange that it starts at all! I'm afraid to set the programmer to turn on the stove when we are not at home! I have already called the service twice and one said that there was a leak somewhere + you need to install an expansion tank and the other one did not find anything, only the radiators were checked. I would like to add that I have just moved into the house and I do not know this stove ... no leaks on the walls are visible. The stove is 10 years old. The second thing is, once in a while, when you turn on the water heating, the S54 code pops up (too fast temperature increase). While the water is heating up, the green light is always blinking + the orange light is on. Help, because I don't know where to look for a solution anymore. Thanks in advance!

MWmalwina wrote:

Slightly above zero it is only when the stove is turned off, when it fires up, the pressure rises to 1 and remains there. If I raise the pressure before turning on the stove to 1.6 bar, it will stay there as long as the stove is running. When switching off, e.g. at 10 p.m., in the morning at 5 p.m. the pressure is slightly above 0 or 0.

I do not know what specific boiler model you have, but I assume something similar to my VUW240 / 2-5.
With a properly operating boiler, you should have, for example, 1.2-1.4 bar on a cold system. After heating the boiler water in the central heating system, the pressure will increase by 0.2-0.3 bar, i.e. not more than 1.5-1.7 bar.
If the pressure is around 0 in the morning, it means that there was a loss of water.
The cause of the loss must be determined.
Quite often the problem is the lack or too low air pressure in the expansion vessel built into the boiler, then the water pressure in the boiler may increase over 2.5 bar and then there is a risk that a safety valve will open through which water may flow to the sewage system. If you have the safety valve connected to the sewage system with a hose, you will not even notice this loss.
There may also be another defect in which the water seeps and the effect is visible after a few hours.

Unfortunately, basic knowledge of the construction and operation of the boiler is needed here so that something can be done meaningfully.
Since the cavity is at night when you are asleep, watch the boiler during the day to find out what is going on.
You can take a photo and upload a photo with a view of the valves located under the boiler, it will be seen if it could be an effect of, for example, a safety valve and at least one element will be excluded.

MWmalwina wrote:

The second thing is, once in a while, the S54 code pops up when you turn on the water heating

Lack of water may result in overheating of the water in the boiler and the temperature sensors register too large temperature differences, which may result in the state S.54.
I have never had one like this on my boiler, because I always keep an eye on the boiler and react immediately after noticing / hearing any irregularities in its operation.
You need to determine the cause of the pressure drop in the boiler and remove it to get rid of the condition S.54

MWmalwina wrote:

While the water is heating up, the green light is always blinking + the orange light is on.

This is normal and correct.
The orange LED symbolizes the working burner, i.e. the presence of the flame.
Flashing green means the boiler is operating in the domestic hot water mode
In the what mode, only the orange LED will be lit.

Thanks very much for the answer, I'll post photos in the evening.
As for the error code, it pops up when the pressure is normal, 1.6 bar, and only when the water is warming up.
He has been watching the boiler during the day for two weeks as it works and no leaks. In the morning I jump up so that it does not run on zero pressure and I pick it up for him ... every morning!

Added after 8 [minutes]:

... and one more important thing, if the boiler starts up from 0, the pressure will rise by itself within 2 hours to 08-1, and if I raise the pressure before turning it on, it will increase to 1.8-2 bar.

And what happens with the pressure when you have 1 bar on the cold one and the boiler will start working?
Does this keep the pressure up to +0.2 bar or does it rise a lot (over 2.5 bar)?
And is the end of the safety valve visible from the bottom of the boiler, is there a hose on it and to the sewage system?
I can see that there is already an answer partially. This is an interesting case and there is probably no way without a kumaty technician.

There was never 1 bar on the cold one, unless I raise it, then during the operation of the stove it will rise to 1.8-2 bar in about 2 hours.

I will come home and take photos of the boiler and connections.

Yes, I understand, the only question is whether we hit 1 bar on a cold one, or whether it increases a lot when heated. And does the pressure remain unchanged until the end of heating and only when it cools down it goes to 0. So we are waiting for the photos.

I add to 1 bar on the cold one, after heating it increases to 1.8 and remains so until the very end of the stove operation.
Example from yesterday ... in the morning at 10 o'clock I punch from 0 to 1, at 12 o'clock it was already 1.7 and it lasted until 22 o'clock ... at 22 the stove turns off. At 4 am I came back from New Year's Eve and it was 0.7 and by 11 it was 0.

MWmalwina wrote:

I add to 1 bar on the cold one, after heating it increases to 1.8 and remains so until the very end of the stove operation.

This is not correct work, because as I wrote before, after heating the water, the water pressure cannot rise by more than 0.2-0.3 bar.

At the outset, I would check the pressure in the diaphragm vessel:
https://www.elektroda.pl/rtvforum/topic938268.html
check the pressure on the open drain valve after draining the water from the boiler.
The manufacturer recommends an air pressure of 0.75 bar.
I keep 1.0 bar in my vessel, the water pressure in the cold system is 1.4 bar, after heating the water pressure jumps to about 1.6 bar and it stays like that all the time.

There may be a problem with the lack of air in the vessel and usually it is enough to inflate it with a car pump, but sometimes the valve is damaged and it needs to be replaced with a new one, the same as in car wheels. In the worst case, if the diaphragm is damaged, it is necessary to replace the vessel with new, original ones, some replacement installed next to the boiler.

If you exclude the problem of the diaphragm vessel and the problem with pressure surges persists, you can look further.

How big are your installations? How many radiators? What heaters? How many m2 of the house? Is the flooring?
The leaks don't have to be visible. A small leak can evaporate somewhere immediately, and only a very careful inspection of all connections by an experienced person can help. I do not put on the diaphragm vessel - because if it were to blame, the pressure increase would be quite fast and would result in water discharge through the safety valve - and you write that it does not get wet anywhere.
You can try to close the CO valves under the boiler for a few hours and see if the pressure drops or not. Thus, we will eliminate the fault of the boiler and the vessel.
Of course, you cannot call for heating then - only hot water.

There are 10 radiators, the house is 110 m2 (ground floor and first floor), there is no underfloor heating.
I closed the main water valve for the whole night when the stove turned off at 10 pm, the pressure drop was.

Not the main one from the water. Only CO valves under the boiler. In Vaillant, there are those on the hexagon

Maybe I'm sending photos, they'll help!

Added after 7 [minutes]:

I marked in red the places where the boiler can be cut off from the central heating system with a screwdriver, preferably a size 4 hexagon
The safety valve is on the extreme right position with a gray knob.
You don't have any hose there, so the safety valve does not run the water out, otherwise it would run out of the valve onto the floor.

In such a system, as zales.vip wrote, it is best to cut off the boiler from the central heating installation
Assuming that the valves are 100% efficient, if you cut off the boiler from the central heating system and the pressure continues to drop to zero, you will know that the problem is in the boiler. If the pressure does not drop it indicates that the pressure problem is somewhere on the central heating side

And, if something can be said, it is best to do it on a cold boiler to minimize the influence of thermal expansion. For example, before going to work in the morning, top up the water pressure and shut off the boiler.
Only colleagues should tell me if they are valves only 90 * turn or turn until the stop.

I am waiting for information on how many degrees I should turn the valve with the hexagon and I will start checking this weekend.
I will let you know what and how!
Thank you gentlemen: - * !!!

The valves are turned 90 degrees, which is a right angle. The screwdriver can be reinforced with a screwdriver, so the best option is an allen key. You turn it as if you were turning the screw, i.e. clockwise and clockwise. We unscrew the opposite ;-)

Added after 2 [minutes]:

It is easy to remember that the slot for the screwdriver will be along the flow of the water when the valve is open or it will be across like a dam when the valve is closed, so you can visualize it like this to tell straight away whether the valve is open or closed.

The valves are designed to prevent more than 90 degrees of movement. So twist it until you feel resistance.
BUCKS is right - preferably with an imbus
As my colleague Wojtermet25 wrote - preferably on a cooled down boiler. Do not forget to turn off the CO function - otherwise the boiler will overheat.
Carefully check all flare connections in the installation. Preferably, any place - especially around radiators, thermostatic heads, angular screw connections by radiators, etc. Slowly - use a flashlight to check it, touching it thoroughly with a dry paper towel - it will show the "truth".

I will just add that in the installation, leaks very often occur on vent valves: on risers (the end of vertical pipes on the top floor) and / or on manifolds (most often metal boxes in which brass beams are placed to which pipes for individual radiators are led - on each floor separately).
The same may be true for an air vent in the boiler installed on the pump.

ls_77 wrote:

The same may be true for an air vent in the boiler installed on the pump

I had a leak a few years ago in the vent that was built into the pump, but it was minor and I noticed it before. It was enough to descale this vent and it still works without any problems.
However, I've never had a leak that would drop the pressure to zero in a few hours, so it's hard for me to estimate how much water would have to flow out for the pressure on the boiler to drop from e.g. 1.6 bar to zero.
It seems to me that such a leak would not have escaped my attention and would have to leave a visible mark somewhere in the installation or on the boiler.

... well, where is the water that I add every day?

BUCKS wrote:

ls_77 wrote:

The same may be true for an air vent in the boiler installed on the pump

I had a leak a few years ago in the vent that was built into the pump, but it was minor and I noticed it before. It was enough to descale this vent and it still works without any problems.
However, I've never had a leak that would drop the pressure to zero in a few hours, so it's hard for me to estimate how much water would have to flow out for the pressure on the boiler to drop from e.g. 1.6 bar to zero.
It seems to me that such a leak would not have escaped my attention and would have to leave a visible mark somewhere in the installation or on the boiler.

BUCKS I got a ban as if what ?

You have not tried to use the pressure check by the so-called water hammer and proper water addition .. sometimes it helps ..

@qr there is no need. A closer inspection showed a leak in the pipes bricked up in the wall, so it is necessary to visit the installer, chiselling the wall, etc.
Also, in total, the author has the worst possible variants, because she is facing an unplanned renovation.

And these pipes are very thick ..? because even worse is getting into the old one .. there may be a problem of lack of space for screw fittings, I went through it myself .. and I do not wish anyone .. or to weld

You have to measure well and take stock ..

BUCKS wrote:

@qr there is no need. A closer inspection showed a leak in the pipes bricked up in the wall, so it is necessary to visit the installer, chiselling the wall, etc.
Also, in total, the author has the worst possible variants, because she is facing an unplanned renovation.

Therefore, it is better if the pipes are not bricked up, but run on the surface (easier locating and repairing failures).

qr wrote:

And these pipes are very thick ..?

copper 22, also I do not see any special problems.

Zbigniew Rusek wrote:

Therefore, it is better if the pipes are not bricked up, but run on the surface (easier locating and repairing failures).

I agree with that, but sometimes aesthetics wins and pipes are thrown into the wall.
I myself have it done in the kitchen, where I have a boiler. It looks nice, but in case of a leak, it's screwed up.
Only in the event that copper pipes are thrown into the wall, it is important that the grout does not come into direct contact with the pipe. I don't know how u is @MWmalwina but everything will turn out when the renovation starts.

The problem has not been solved yet, but the users directed me to the methods of solving it.