Operation of gravity primaries

[benmaye]

on a pumped heating and gravity hot-water system, what device controls the operation of the gravity primaries?

 

[cider]

Heat from the boiler

 

[benmaye]

No. What device operates it, i.e. Motorised valve, Room thermostat.. etc

 

[david17uk]

cylinder stat + boiler stat

 

[namsag]

As cider says it works through convection and its only usually the boiler stat that controls it from gettin too hot

 

[david17uk]

The boiler stat controls the temperature of the water in the coil and flow and return pipework.

The cylinder stat controls the temperature of the stored water in the cylinder. When you run a hot tap, hot water leaves the top of the cylinder and is replaced by cold water from the tank.

When the cylinder stat senses the water being below it's set temperature (60-65 degrees), the boiler will fire up.

 

[Tipper]

But you can add a cylinder thermostat which shuts the boiler down when the tank is full and CH not calling for heat.

Or fit a motorised valve as well to stop the gravity circulation when the tank is full.

If you want to boost the gravity circulation to reduce the reheat time you can fit an additional pump controlled by the cylinder thermostat, with or without the above.

 

[JohnD]

very often, a gravity HW primary does not have a cyl stat, so the only control is the boiler stat and timer. Whenever the CH is running the cyl is heated. This is quite wasteful, also the primary pipes are needlesly hot much of the time.

rarely, the primary return from the cylinder has a Cyltrol valve or a Drayton Tapstat valve (both rather expensive); it stops the water flow when the cyl is hot, but does not stop the boiler firing.

 

[benmaye]

yes but isnt it the room stat that detects enough heat? or is the device the motorised valve that phyically shuts down the primaries?
They both control the operation, one electrically and one physically!!

 

[david17uk]

Your getting mixed up with the heating side of the system

If your house is warm (room stat), you'll still need hot water

 

[davebgas]

clue is in your post title........ 'gravity primaries' why would a room stat control these???? the CH will operate on a pump and the heat exchanger will have 4 tappings......2 on the pumped CH (with room stat) and 2 on the gravity primaries.....

 

[benmaye]

ahh. of course, thanks guys. I was reading it incorrectly re: the room thermostat. The motorised valve is what I was looking for.
cheers, much appreciated