Gravity hot water to fully pumped / sealed

[John.g]

might be best to start a new thread as im sure theres more people who would like to learn this information

Thanks John. I was overlooking thermal expansion coefficient on the left of boxes
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How would an expansion vessel under charged at ground floor level affect circulation in upstairs rads on start up @John.g?

I'll just answer this and maybe some one can/would transfer these posts to a appropriate thread.

If, for any reason, the pre pressure and fill pressure (due to leakage or improper charging or whatever) fall below the static head then the water level will start falling in the upstairs rads (first) and because the circulating pump is just that, a circulating pump, eventually there will be no circulation upstairs, after start up , and depending on the water temperature, the EV pressure will start to rise and may provide enough pressure (head) to allow circulation through these rads again. IMO poor or failed upstairs rad circulation is a indication of EV/water leakage problems.
Or to put it another way, if you pre charged to say 0.3 bar and initial filled to 0.3 bar then IMO there will be no upstairs circulation.

 

[eagleeye]

One of our installers currently fitted a new heat only boiler to replace an old floor standing with gravity hot water. At the time he never fitted any valves or cylinder stat etc so I have been called back there to basically start again. Been there today to do it and found that he had the pump on the return. Anyway I drained system and made the necessary alterations to the pipework by the boiler and fitted a mid position valve and a wireless cylinder stat (as the run is impossible to get a cable between the two). So currently the feed from the F + E tank goes into the return of the cylinder and the vent on the flow. The boiler is in a tight cupboard low to the ground in an extension of the side of the house and the cylinder is on the 1st floor in the middle of the main part of the house so you can imagine how the pipework runs

Hi all just thought id update you with todays result. So i did what i thought was best and fitted and 18 ltr vessel above the boiler, took out the f + e tank and fitted AAV's on the feed and vent pipes from the cylinder coil. works an absolute treat.

 

[SJB060685]

Yes I understand how low water pressure can result in no circulation of upstairs rads, especially when you say it's a circulator and not a lifter which some people misconceive. I had however overlooked low EV pressure and it possibility acting as an accumulator

 

[John.g]

Hi all just thought id update you with todays result. So i did what i thought was best and fitted and 18 ltr vessel above the boiler, took out the f + e tank and fitted AAV's on the feed and vent pipes from the cylinder coil. works an absolute treat.

So now, a fully sealed system.

 

[eagleeye]

So now, a fully sealed system.

yes and the best way. do like your info on the other way though but why mess about with that when its just as easy to seal it isn't it ?