Hot water from Tundish after multiple checks.

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John. I have attached the schematic from the Santon cylinder installation manual. It shows the balance cold water connection tee to come after the combo valve and PRV and before the EV tee. I have also attached a photo of the actual set up reflection those instructions with the balanced out after the combo valve and PRV. Are you saying there should be a non return valve installed on my system somewhere, Im not convinced I have one fitted? can you advise from my photo?

On your second query, I think the PRV combo valve was intec or intatec. How would I know if the PRV was drop tight.? Once again, would increasing the size of the expansion vessel to 25l (6l) greater than I currently have alleviate the pressure causing the Pressure release valve to open? I notice when the the boiler is on and the tundish is leaking, the pressure via my little Schrader gauge literally tops out and is at least 6-7 bar? its set to 3 bar when empty.
 

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You don't seem to have a combination valve set, you have 2?? PRVs followed by a expansion relief valve, followed by the teed off balanced cold.
It's easy to check if the PRV is passing, with no heating scheduled, just run off say 5L of HW, then immediately take your pressure reading, ensure no HW or balanced cold draw off for say 1 hour if possible then retake the pressure reading.

You will require the full details of the PRV to establish if its drop tight or not.
 
The lower PRV was fitted years ago by a plumber who I had called in because our water pressure was causing a lot of noise when running taps etc throughout the house. When he came, he said our pressure was too high and fitted that lower PRV. I did not know the system as I would now to debate if that was right or wrong, but I can appreciate now, that the PRV he fitted was not needed as there was already one on the Combo valve. They are both set to 3 bar so shouldn't be causing any issues. (thats part of my mistrust getting people in to do these jobs, Ive been burnt so many times unfortunately)
The Combo valve that failed and had to be replaced last week was as per the photo. It was a Santon 95 605 863. this was discontinued. The plumbing supplies shop supplied me with the one now fitted as per the photo. It has a filter and pressure relief valve in it, and the pressure release valve is separate and below. Im not sure if there is a non return valve in it. This always been the set up from new?

I'll check the PRV by running off the hot water for 5l as you suggest then recheck. I'll post back. Thanks for you help so far. Is anything indicating what might be my issue with the PRV expelling hot water given the details supplied so far?
What would your synopsis be. Also, as per earlier question, do you think a 25l exp. vessel might help?
 

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Couldn't reply yesterday for some reason or other.

The issue of expelling HW is either caused by a failed EV (ruled out?), improperly precharged EV pressure due to faulty pressure "gauge"?, or PRV passing with no demand for HW or balanced mains beig pressurized from mains or mixer.
A 19L EV is perfectly suitable for your 210L cylinder, a 25L will not cure your existing problem.

You test will tell a lot.
 
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Yes, I'm sure the EV is fine. It holds a charge ok and is only a few years old. I measured the pressure on the Ev bladder with 3 gauges. A new one I bought a few days back, 1 I already had, and the gauge on the tyre inflator I have for my compressor which is a heavy duty forecourt job. All are measuring pretty much the same at any given point.

The third point you raise above is the unknown. The 6 bar PRV is undoubtedly discharging hot water when there is no demand, and more noticeable during and after the hot water has been heated by a boiler cycle. It can be temporarily stopped by running a hot tap, or either the hot or cold side of the shower mixers. Eventually however, the PRV will start dripping again, as if pressure starts to build back up in the system after a while?

Im waiting on the pressure reading after the 5L test. Wife keeps turning taps on and off before the 1 hr mark! I'll get that done today.

What's killing me, is that I am convinced there is an easy fix here somewhere.
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