Semi gravity system - layout?

[jackecole]

With a semi gravity system (gravity H/W) and pumped heating, and the heating having an anti-gravity valve after the pump, is there 2 vent pipes (1 for H/W and 1 for HTG) and 2 cold feeds?? Usually semi-gravity systems have 4 tapping-boilers don't they??

 

[buck51]

In a word yes they do,

 

[jackecole]

ok thanks for that - must be weird seeing 2 vents going over the header tank!!

 

[doitall]

With a semi gravity system (gravity H/W) and pumped heating, and the heating having an anti-gravity valve after the pump, is there 2 vent pipes (1 for H/W and 1 for HTG) and 2 cold feeds?? Usually semi-gravity systems have 4 tapping-boilers don't they??

No, there's only one cold feed and vent pipe on the gravity circuit or direct to the boiler.

Depends the the size of the boiler, larger boilers have 4+ connections, smaller boilers can have 2 with a special pipe arrangement.

All new installs must be fully pump.

 

[buck51]

You should also have two tanks one for heatingsystem and one for cold water feed to the hot water cylinder

 

[doitall]

You should also have two tanks one for heatingsystem and one for cold water feed to the hot water cylinder

The OP is talking about the primary water, and not the secondary water.

I think

 

[jackecole]

Thanks for your info.... I guess as long as the anti-gravity valves are after the pump then it would have been fine with only HW on (ie in summertime).

If you replace a HW cylinder or a boiler on a semi gravity system can you still have the HW gravity, and just use a thermo mechanical stat (ie Drayton Tapsat) or do you need a cyl stat and MV ???

 

[buck51]

Its hard work reading between the lines aint it!!!

 

[doitall]

You can replace a cylinder like for like, if however you replace a boiler the system should be up-graded to fully pumped.

There's various valves that can be fitted in the primary return circuit, the flow/vent must remain open to atmosphere.

 

[jackecole]

I see, a new boiler would mean a cyl stat and a 2port (MV) for the hw circuit as well as the HTG circuit, but a new cylinder only then a tapstat would be allowed.

 

[doitall]

Controls of any sort are always advisable when changing a cylinder, but not, a requirement.