C-PLAN hot water valve?

[stevehayes]

a quick question - why is the motorized valve (2-port) on the Return between the cylinder and boiler on a c-plan system (gravity hot water) - why can't it be on the flow? Does it make a difference? Was reading about it and it didn't state why! WOuld be interesting to know if anyone knows why?

 

[ChrisR]

When valves are put in the trturn it's often to keep the route between the boiler and the vent clear. No valves allowed there.

 

[namsag]

Bcause the vent pipe is on the flow and cannot have any valve on it at all. Try reading a bit more

 

[stevehayes]

i know the vent is on the flow side, and obviously no valves should be on it, so i get your point. also the cold feed from the f & e on a c plan joins the primary return from the cylinder and no valves must be on this either! if the 2 port was after the vent T but before the cylinder instead of after the cylinder and before the feed then surely it would be better? i mean if it's on the return and the heating is on and not the hot water then heat will still rise to the cylinder, which has closed it's retrun path- thus making the stored hot water excessively hot???!

 

[namsag]

If the heat cant circulate then it will not add anymore heat to cylinder.
Most gravity circuits would not have the room to put it on the horizontal after tee as you suggest, but can`t see any reason why not if there is the room, not to say that there maybe a rule but cant think of one

 

[stevehayes]

good point about water not circulating preventing the heat increase. i suppose as you say there is more room on the return between the cylinder and when the cold feed enters. thanks for your help on this. is it also true that an injector tee MUST used on a solid fuel boiler when gravity hot water and pumped heating returns are returned to the boiler via a common return pipe? so a 3 tapping boiler instead of a normal 4 -tapping boiler for solid fuel?

 

[Softus]

is it also true that an injector tee MUST used on a solid fuel boiler when gravity hot water and pumped heating returns are returned to the boiler via a common return pipe?

Generally, yes, but the boiler manufacturer will stipulate how it's installed in terms of injector tee, length and gauge of primaries, pipe thermostats, pump behaviour etc.

so a 3 tapping boiler instead of a normal 4 -tapping boiler for solid fuel?

Eh?

The boiler needs only two tappings - the gravity return and the heating return meet at the injector tee.

 

[stevehayes]

solid fuel boilers can also have a separate flow for both heating and hot water circuits.

 

[Softus]

My point was that it will have either two or four tappings, not three.

 

[stevehayes]

yes you're right, if using 3 then the 4th tapping will be capped off. as you say though 2 will more than likely be used nowadays anyway.

 

[tim-spam]

To answer your original question, the motorised valve can be fitted to either the flow or return (between the tee and the tank of course), but it is better in the return because it's cooler - simple as that. In most installations nowadays, there will probably be some re-plumbing needed to make space for the valve.

 

[warmadmax]

my baxi back boiler has 3 tappings,
with the HW return injector teed into the CH return

i thought the reason for not blocking the HW flow was to ensure if the boiler was running away thermally, the expanding hot water could escape up the vent pipe without any restrictions,
the boiler instructions state there must be no valves between the vent exit and the boiler, a zone valve would comprimise this.

the valve would mean the HW has to escape via the injector tee, at the bottom of the heat exchanger, this would only occur after pressure has built up behind the closed valve.