Hot Water Pressure Problem Eco Tec Plus 831 Vaillant Boiler

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I had this boiler installed about 3 years ago and have had no issues. About two weeks ago I put the heating back on and it seems to have impacted on the hot water pressure which has become very weak.
I have had two engineers out to look at it and they keep blaming the mains. I know this is not the case. Before the pressure dropped F22 came up on the box. This has now gone.
I have had the heating switched off and the pressure to a certain extent has come back, although it is still not as powerful as it was.
I switched the heating on again yesterday morning and the pressure on the hot water had gone again.
I spoke with another engineer and he mentioned a part which may be faulty (apparently a common problem with the Vailliant boilers), something about it getting hot and so it stopping the hot water pressure?? I can't get in touch with this engineer again...
I have another engineer coming out again on Thursday and am looking for any help or advice about what might be wrong. Any suggestions?
 
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Do you understand what pressure is?

How are you measuring the hot water pressure?

Why are you having all these engineers out? Two so far and another on Thursday! You have also spoken to another!

Presumably you are paying them for their callout?

Can you explain whats going on?

Tony
 
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I have had two engineers out to look at it and they keep blaming the mains. I know this is not the case.

To know that is not the cause, you will have measured the dynamic pressure from the mains.

What pressure at what flow rate do you get?

I take it that you do really understand pressure, flow and dynamic pressure?

Tony
 
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I am not paying because it is covered in the maintenance contract - thank god. It has to be a problem with the boiler as it is directly effected when the heating has been on.
What I mean by the pressure is, when I turn the shower on the force of the water which comes out is now very low. Does that make sense?
I have checked the pressure gage on the boiler and that is fine, there is no drop on that at all.
Thanks for your quick response.
 
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Pressure is measured with a pressure gauge!

With the same shower AND the same mains supply pressure from the street then the only change the boiler could potentially make is to reduce the FLOW rate!

I suggest you measure and continually monitor the mains water supply pressure!

And if you like to measure the flow rate through your shower.

But to eliminate the shower itself you would need to measure the flow rate from a hot tap as well!

Why do you think its the boiler and not the shower or just the mains supply pressure?

Tony
 
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I think I may have the answer, When the heating is on and hot, is the pressure gauge touching the red? If so, the problem is your expansion vessel is depleted. To explain, when the pressure is too high, the boiler will not go to high gas, Your themostatic shower is reducing the flow to try and get hot water for you.

Get yourr engineer to check this, if he i unaware of this 'fault' , it is only the latter software versions of the PCB that do this.
 
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I haven't really noticed it with the hot taps as I don't tend to have these on for any amount of time. Although yesterday I did run a bath and it took forever to fill, again because of the lack of hot water pressure.
The cold water pressure is always fine though.
 
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is it the same with hot taps .

I haven't really noticed it with the hot taps as I don't tend to have these on for any amount of time. Although yesterday I did run a bath and it took forever to fill, again because of the lack of hot water pressure.
The cold water pressure is always fine though.
 
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I think I may have the answer, When the heating is on and hot, is the pressure gauge touching the red? If so, the problem is your expansion vessel is depleted. To explain, when the pressure is too high, the boiler will not go to high gas, Your themostatic shower is reducing the flow to try and get hot water for you.

Get yourr engineer to check this, if he i unaware of this 'fault' , it is only the latter software versions of the PCB that do this.

I think this is what the other engineer initally said, the two who have come out didn't know what I was talking about, but I will tell them about this. Thanks for your help!
 
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Pressure is measured with a pressure gauge!

With the same shower AND the same mains supply pressure from the street then the only change the boiler could potentially make is to reduce the FLOW rate!

I suggest you measure and continually monitor the mains water supply pressure!

And if you like to measure the flow rate through your shower.

But to eliminate the shower itself you would need to measure the flow rate from a hot tap as well!

Why do you think its the boiler and not the shower or just the mains supply pressure?

Tony

The hot taps are exactly the same. The pressure goes on them when running a bath. I think it is the bolier as it is directly linked following an error code (which admittedly has now gone) and when the heating has been on.

Thanks for your help!
 
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The boiler has no means of altering the hot water pressure dynamically.

The pressure out of the hot tap will be influenced by what you are using via the cold tap, but not whether you have the heating on, or what the pressure is on the display.

The comment about the expansion vessel may be correct, but it will not affect the pressure from a tap, only the temperature you obtain.

There is an line filter on the hot pipe, but this would consistently lower the performance if it were partially blocked.
 
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I think I may have the answer, When the heating is on and hot, is the pressure gauge touching the red? If so, the problem is your expansion vessel is depleted. To explain, when the pressure is too high, the boiler will not go to high gas, Your themostatic shower is reducing the flow to try and get hot water for you.

Get yourr engineer to check this, if he i unaware of this 'fault' , it is only the latter software versions of the PCB that do this.
this is deffo a new one one on me, early or late eco's all work the same, if the system pressure is to high the pressure sensor wont see a change and fault f.75 never have i seen or heard of it holding the boiler on low fire or reducing the dynamic in the hot(impossible),
my tupence worth is blocked or reduced flow rates not presure as the op doesn't understand dynamic and standing presures and seems to be talking f/r's!!
 
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another thought to this is that extremely high pressures around 10 bar + eliminate flow restrictors on ecotecs and therefor allow a higher flow than prescribed thus reducing temperature gain of 42 deg as said in book!
possibly to high a flow rate in other words!
 
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Hang on folks!

The lady seems to be using the word "pressure" when she really means "flow".

Someone needs to measure the flow rates from taps and shower!
 

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