[Solved] No Hot Water in Boiler: Issues with Mixing, Pump Overflow, Heating & New 140L Boiler Replacement

Good morning,
I have a problem with domestic hot water recently. after extinguishing the oven at 22.00, at 5.00 there is no hot water, there is no even lukewarm, it is only cold. The reason for this was that the boiler was to be damaged. The plumber said the possibility of mixing water from the central heating system with water supplying the boiler. during operation of the furnace, the pump could be heard as if water inside the boiler was overflowing. until now there was no problem with hot water, you could always bathe in the morning. the boiler was replaced with a new one (the old one was 100l, new 140l), the problem did not disappear, after the furnace was turned off cold water in the morning. in addition, by burning in the oven all day and maintaining a temperature of about 70 degrees, the water heats up very slowly and after dropping a small amount (two people shower), the water cools down very much. installation is very simple, without any valves on the supply and return from the boiler (it was never and it was ok), water pump, expansion tank. radiators heat up correctly, there is no problem.
I ask for advice.

Do you have a pump with a boiler controller?

no drivers. the pump works in the whole central heating installation and I turn it on from my hand, when the temperature reaches e.g. 50 degrees on the stove I turn on the pompom and hula around the house. everything worked fine for about 10 years.

Show installation photos.
You don't have air coils? If the boiler supply pipe is at the highest point of the installation (connection to the riser below), a vent must be installed on it.

the breather is installed, the double-shell tank, piece-by-piece exchanged, same connection. I thought maybe it was connected the other way around, but no, everything is as before. I thought the boiler is not filled with water, but there is water without air from the tap. boiler supply and return - hot pipes. the water is also hot, but after draining a dozen, maybe thirty liters, the water cools down, the temperature on the boiler drops.

Grzegorz Czapka wrote:

everything worked fine for about 10 years.

It is likely that the boiler feed pipes have crumbled and the water does not flow as fast as before.
Hence the problem with fast dhw heating

Added after 1 [minutes]:

if there was a mess, why is the supply and return from the boiler hot pipes? and how to clean this crap? pour some agent for installation?

Added after 2 [minutes]:

by the old boiler it was heard all the time, as if water and air were flowing in it, but it was like that for as long as I can remember until there was a problem with the water cooling quickly in the boiler.

Grzegorz Czapka wrote:

if there was a mess, why is the supply and return from the boiler hot pipes?

This is a symptom.
The sludge clogs the pipes and creates thermal insulation from the inside of the pipe.
Which hinders heat exchange and fast heating of the boiler.
But if the boiler was recently replaced, this problem should not occur.
Also the boiler feed pipes can be clogged, as if you installed a valve there and opened it for 1/4 .

the boiler was replaced three days ago and there is no effect. with the old water in the morning was cold, but in the evening four people could bathe in warm water. now after replacing the boiler, in addition to the fact that there is no hot water in the morning, only two people can take a bath in the hot water in the evening. I will only add that the old boiler had a capacity of 100l, the new boiler has 140l. I already thought that this is the reason that the stove is not efficient and cannot heat up the water, but if it burns all day and drains 30l of water and then it is only lukewarm, then probably the fault is not on the boiler capacity.
How to get rid of sludge from the installation?

@__Grzegorz__ Czapka

There was a coil in the old boiler?

the old boiler is also a double jacket. same connection. As I wrote earlier, there was a suspicion that it is leaking inside and the water mixed with water from the power supply and that's why I replaced the boiler. I haven't checked if the old one is actually damaged.

Grzegorz Czapka wrote:

As I wrote earlier, there was a suspicion that it was leaking inside and water mixed with water from the power supply

If the boiler were leaking inside, you would have more water in the central heating system and would overflow.
Why the hell do you have a valve under the vent closed? Open it because the boiler cannot vent.
The old boiler was certainly good, only a broken plumber. You didn't have hot water in the morning because the boiler cooled by gravity.

The valve was closed temporarily, because I was replacing the vent, it is generally open. I replaced the boiler, because it was the "plumber" recommendation. as I wrote earlier, you could hear water pouring from one vessel to another. I agree that the water in the morning was cold because it was cooling by gravity. So how do you explain the fact that she hasn't cooled down in ten years, and it has started to do so recently. nothing in the installation was changed except a pump that broke and didn't mix water. the installation may not be the latest, but it has been effective so far and has worked flawlessly with my parents. today dad informed me that the water was hot in the morning. what he did:
a) turned off the ball valve in the return co
b) but interestingly, turned off the supply of running water to the boiler, causing that the tap did not run hot water. It may be a bit strange, but Dad's trial and error method works. Does turning off the tap water supply to the boiler have anything to do with keeping the water warm?

Added after 37 [seconds]:

The valve was closed temporarily, because I was replacing the vent, it is generally open. I replaced the boiler because it was a "plumber" recommendation. as I wrote earlier, you could hear water pouring from one vessel to another. I agree that the water in the morning was cold because it was cooling by gravity. So how do you explain the fact that she hasn't cooled down in ten years, and it has started to do so recently. nothing in the installation was changed except a pump that broke and didn't mix water. the installation may not be the latest, but it has been effective so far and has worked flawlessly with my parents. today dad informed me that the water was hot in the morning. what he did:
a) turned off the ball valve in the return co
b) but interestingly, turned off the supply of running water to the boiler, causing that the tap did not run hot water. It may be a bit strange, but Dad's trial and error method works. Does turning off the tap water supply to the boiler have anything to do with keeping the water warm?

Grzegorz Czapka wrote:

but interestingly, he turned off the supply of running water to the boiler, causing that the tap did not run hot water. It may be a bit strange, but Dad's trial and error method works. Does turning off the tap water supply to the boiler have anything to do with keeping the water warm?

So the heated water from the boiler is flowing all the time.
So you have a hole in the pipe, on the section boiler-taps.

As for closing the return on the stove what, this applies to radiators with the boiler?
Does the circuit close only on radiators?

I sense the latter option, otherwise it doesn't make sense.

I don't suppose holes, because there is no leakage anywhere, today we will check what will happen when the valve that cuts off the water supply is open. yes, the valve closes the circuit for radiators, a small circuit remains - stove - boiler. we are waiting for some magician to embrace this topic because we are running out of ideas one more thing bothers me, when the pump turns on, the water can be heard in the boiler, as if with air, maybe this boiler is still airy and therefore does not heat up and does not keep hot water. only where does this air come from and how to get rid of it. vented radiators, because they heat all on two floors, the furnace does not reach high temperatures, which is also ok, and still a lime with a boiler.

Grzegorz Czapka wrote:

I don't suppose holes, because there is no leakage anywhere,

I did not let the leak at home, but still.
The pipe was run into the basement floor, which turned out to be corroded and leaked.
In this situation, water flows through the boiler all the time, which prevents the water from heating up.
It's like leaving a tap turned on.
One more thing, turn off all the taps and watch the counter if it turns and there is a strange passage.

I go to my father and keep trying, if we manage to do something, I will let you know, thank you for all the hints. one more thing, when there was an old boiler, you could hear (as I wrote earlier), as if water overflowed, all the time. after installing a new boiler, the overflow disappeared, only when the pump turns on, you can hear the movement of water.

Leaking battery between cold and warm?
In the photo on the thermometer you can see cold water, hot water is when the pointer is close to the vertical. This thermometer is not precise enough.
The boiler is in the next room, and the inch pipe on the first tee behind the pump in a straight line goes to the boiler? By the way, how did you pass the chimney? In general, the error is that the pipes are almost perfectly horizontal. The vent connection is a book example of incorrect installation. The system may still be aerated. Return from the boiler should be warm.

thank you all for the hints, it helped me determine the cause of the water cooling. there is no error in the installation, because the installation itself has been working for about 30 years , and the boiler was added about 10 years ago, everything was working properly, until it broke. The problem is that I diagnosed a leak of hot water from the pipe in the bathroom wall. this is the reason for water cooling, bathroom renovation is waiting for us thank you for the hints, especially for RESISTOR 240.