Hello, for the first 2 to 3 seconds the pressure in our domestic hot water line is very high and then stabilizes. What could be the cause? We have an air-to-water heat pump. I have attached some pictures showing individual valves. Could it be related to these? I am concerned that this issue might negatively affect the heating system. The pressure only builds up again afterwards. If I use hot water again shortly after, the pressure is normal. We do not have continuous circulation.
What is the water pressure in your house? What does high hot water pressure mean?
Static pressure is always higher than flow pressure.
The greater the pressure and the smaller the maximum flow rate, the more noticeable this effect becomes.
This can be mitigated with expansion tanks.
The heating system does not play a role in this. The usual water pressure is not a problem.
Just as an example: In our case, the supplier did not properly tap into the main water line in the street. We had almost 5 bar (72.5 psi) pressure. As soon as we opened a tap, the pressure dropped to below 1 bar (14.5 psi). Naturally, hardly any water flowed.
Now, our flow pressure is almost the same as the static pressure.
Static pressure is always higher than flow pressure.
The greater the pressure and the smaller the maximum flow rate, the more noticeable this effect becomes.
This can be mitigated with expansion tanks.
The heating system does not play a role in this. The usual water pressure is not a problem.
Just as an example: In our case, the supplier did not properly tap into the main water line in the street. We had almost 5 bar (72.5 psi) pressure. As soon as we opened a tap, the pressure dropped to below 1 bar (14.5 psi). Naturally, hardly any water flowed.
Now, our flow pressure is almost the same as the static pressure.
@rick2018 Phew, good question. Unfortunately, I can’t tell you what the water pressure is in our house. Where could I check that?
By hot water pressure, I mean the following:
When I run cold water from the tap, everything is normal. The pressure stays constant, and I can wash my hands under the flow without any issues. I would say the water pressure is coming directly from the mains, similar to what I’m used to in other households.
When I open the tap for hot water, the pressure is noticeably higher for the first few seconds. Washing hands without splashing isn’t possible then. After 2 to 3 seconds, the pressure drops to the same level as cold water. Afterwards, I can watch the pressure slowly build up again. After 5 minutes, everything seems normal. After 30 minutes, the pressure is slightly higher again. After a few hours, the pressure is noticeably stronger once more. (Times are roughly estimated here)
By hot water pressure, I mean the following:
When I run cold water from the tap, everything is normal. The pressure stays constant, and I can wash my hands under the flow without any issues. I would say the water pressure is coming directly from the mains, similar to what I’m used to in other households.
When I open the tap for hot water, the pressure is noticeably higher for the first few seconds. Washing hands without splashing isn’t possible then. After 2 to 3 seconds, the pressure drops to the same level as cold water. Afterwards, I can watch the pressure slowly build up again. After 5 minutes, everything seems normal. After 30 minutes, the pressure is slightly higher again. After a few hours, the pressure is noticeably stronger once more. (Times are roughly estimated here)
Hello, I’d like to revisit this topic.
In the meantime, I have gathered some more information.
Our heating system’s boiler is designed for up to 10 bar. The safety valve installed by the technician is also rated for 10 bar. The incoming pressure from the network is 4 bar at our location.
Should the shut-off valve be replaced with one rated for 8 bar? Would that make a difference? It’s not an official defect if the boiler can handle up to 10 bar and the shut-off valve is also rated for 10 bar. But could it be that the pressure in the hot water line after heating is too high because of this?
I want to preserve the components as much as possible, so I am considering replacing the shut-off valve. Or do you think it wouldn’t make any difference?
In the meantime, I have gathered some more information.
Our heating system’s boiler is designed for up to 10 bar. The safety valve installed by the technician is also rated for 10 bar. The incoming pressure from the network is 4 bar at our location.
Should the shut-off valve be replaced with one rated for 8 bar? Would that make a difference? It’s not an official defect if the boiler can handle up to 10 bar and the shut-off valve is also rated for 10 bar. But could it be that the pressure in the hot water line after heating is too high because of this?
I want to preserve the components as much as possible, so I am considering replacing the shut-off valve. Or do you think it wouldn’t make any difference?
rick2018 schrieb:
The hot water pressure is usually the same as the regular water pressure.
The boiler and valve are all fine.
Try partially closing the hot water pipe. That should reduce the water flow slightly at the beginning. Should I control that using picture 3?
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