Hot water venting into header tank, this issue not covered on previous posts

[karlrich1]

Hi all, I'm new to this forum, I apologise if I miss any protocols

My issue on the face of it has been covered many times, but specifically in this instance it makes no sense and I have not yet found a reasonable answer, if you can help it would be very much appreciated.

I have an open vented CH/HW system. For some time there has been a reasonable trickle of hot water being emptied into the header tank via the vent. The pipework is installed correctly, the vent and the cold feed are less than 150mm apart, and in the right sequence from the boiler outlet.

What makes no sense to me as that this ONLY happens when the HW is demanded of the boiler and the Y valve is set to provide both CH and HW. if there is NO demand for HW then the vent remains dry (CH on full tilt)

Given that when there is a demand for both HW and CH the water has more pipework to flow around and therefore the pressure should be reduced, therefore making the overflow LESS likely, So why is this happening?

I have carried out many power flushes, treatments of all kinds - today I have bled the system right down after 2 days of sentinel 800 and still the problem persists.

It happens on pump speed of 2 or 3, and my vent pipe is the correct height above the header tank.

Thanks.

 

[karlrich1]

That's it and for interest you might try it on CH, HW & HWplusCH. (On PP3 mode, top green light flashing)) it should make for interesting reading.
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Just to be clear again after you keep that button depressed for >5 secs the led will start flashing you can then change to PP1 orPP2 or PP3 , I 'm only interested in PP3 mode, top green light flashing. Switch back to fixed speed (solid green light and FS2 selected. (a solid,second green light)
It's explained far better in the UPS2 file that I attached in a previous post.
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OK:-

PP3 pump mode - CH on only from cold start up, the pump used 165W, which as the temperature rose went down after about 20 mins to 13W. Turn on the HW in addition and the steady state was around 9W. Turn off the CH (so now HW only) and it was still around 9W.

During all of this the pump was running far slower than on fixed speed. When the HW was ON the outlet coil to the return from the tank never got hot.... suggesting that was too slow, and the rads took a long while to heat.

I then switched to fixed speed 2 with both CH and HW on and the pump ran at around 42W.

Having never known I had a PP function on my pump - should this be what I ought to run on to save energy?

 

[John.g]

OK then... 16.5W on PP3 equals a flow of ~ 10.5 LPM @ 1.8M, and on your selected fixed speed 2 (5M) equals a flow of 15.8 LPM @ 4M and that IMO is quite satisfactory and will give a deltaT of only 10C across a 11 kw boiler and even if you ran the boiler at 18 kw would result in a deltaT of 16.3C so there really should be no issues with the boiler controls under any of the above conditions.
The 9W on PP3 equals a flowrate of ~ 7.5LPM @ 1.5M which should equals a flowrate of 12.9 LPM @ 4.5M on your selected fixed speed 2 (5M).

PP mode does save a nice bit of power, in my case (14W vs 21W) on a 4M PP setting but unfortunately the UPS2 is one of the poorest choices for PP control as it just doesn't provide a high enough head setting, the 3 settings are 3.0M,2.8M and 2.6M and any pump should be able to provide a PP setting of at least 4.0 to 5.0M to give adequate flow as ideally one wants a PP setting high enough to give you the required flow with everything opened up, it will then throttle back as TRVs or zone valves are closed, ironically, if you had a PP setting of 4.5M on the UPS2 then you would get exactly your required initial flow of 15.8 LPM @ 4M instead of the "miserable" flow of 10.5 LPM @ 1.8M. Granted, the UPS2 PP settings will work where you have a very low loss system or where you might use zone pumps instead of zone valves.
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Jut looking at your results there again, it's a bit strange that you are getting only 9W on PP3 with both HW only on and (9W) HW+CH on together especially since you are getting 13/16W on CH only.
If you get the time (and inclination) you might just take the PP3 reading and the F.speed setting 2 readings with HW only on.

 

[RoryD]

Hi all, I'm new to this forum, I apologise if I miss any protocols

My issue on the face of it has been covered many times, but specifically in this instance it makes no sense and I have not yet found a reasonable answer, if you can help it would be very much appreciated.

I have an open vented CH/HW system. For some time there has been a reasonable trickle of hot water being emptied into the header tank via the vent. The pipework is installed correctly, the vent and the cold feed are less than 150mm apart, and in the right sequence from the boiler outlet.

What makes no sense to me as that this ONLY happens when the HW is demanded of the boiler and the Y valve is set to provide both CH and HW. if there is NO demand for HW then the vent remains dry (CH on full tilt)

Given that when there is a demand for both HW and CH the water has more pipework to flow around and therefore the pressure should be reduced, therefore making the overflow LESS likely, So why is this happening?

I have carried out many power flushes, treatments of all kinds - today I have bled the system right down after 2 days of sentinel 800 and still the problem persists.

It happens on pump speed of 2 or 3, and my vent pipe is the correct height above the header tank.

Thanks.

If I'm seeing your pics correctly, I'd say it is NOT configured correctly. Without running along the horizontal before attaching cf and vent pipes can cause this problem. Fit an air separator instead. As sludge begins to build up flow does get restricted.

 

[John.g]

OK then... 16.5W on PP3 equals a flow of ~ 10.5 LPM @ 1.8M, and on your selected fixed speed 2 (5M) equals a flow of 15.8 LPM @ 4M and that IMO is quite satisfactory and will give a deltaT of only 10C across a 11 kw boiler and even if you ran the boiler at 18 kw would result in a deltaT of 16.3C so there really should be no issues with the boiler controls under any of the above conditions.
The 9W on PP3 equals a flowrate of ~ 7.5LPM @ 1.5M which should equals a flowrate of 12.9 LPM @ 4.5M on your selected fixed speed 2 (5M).

PP mode does save a nice bit of power, in my case (14W vs 21W) on a 4M PP setting but unfortunately the UPS2 is one of the poorest choices for PP control as it just doesn't provide a high enough head setting, the 3 settings are 3.0M,2.8M and 2.6M and any pump should be able to provide a PP setting of at least 4.0 to 5.0M to give adequate flow as ideally one wants a PP setting high enough to give you the required flow with everything opened up, it will then throttle back as TRVs or zone valves are closed, ironically, if you had a PP setting of 4.5M on the UPS2 then you would get exactly your required initial flow of 15.8 LPM @ 4M instead of the "miserable" flow of 10.5 LPM @ 1.8M. Granted, the UPS2 PP settings will work where you have a very low loss system or where you might use zone pumps instead of zone valves.
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Jut looking at your results there again, it's a bit strange that you are getting only 9W on PP3 with both HW only on and (9W) HW+CH on together especially since you are getting 13/16W on CH only.
If you get the time (and inclination) you might just take the PP3 reading and the F.speed setting 2 readings with HW only on.

Any update on your settings now and is the system OK?.