Gravity HW questions/regulations?

[poolebybirth]

Can anyone help me with a few questions regarding gravity fed hot water please?


With a C-PLAN (gravity hot water & fully pumped heating) - is a 4 tapping boiler required or can a standard 2 tapping boiler be used?

Obviously there will be an anti gravity valve installed somewhere after the pump and before the 1st radiator on the circuit so when HW only is required, the radiators do not heat up too.


Also: is a cylinder stat and a 2 port zone valve allowed with gravity HW fed by a solid fuel boiler or is this only allowed for gas and oil boilers with gravity HW due to the solid fuel heat leak that is required? Or with a solid fuel boiler is a cylinder stat allowed by no HW zone valve, again due to the heat leak requirement?

Anyone sure of the exact regs on these issues? Thanks for any help.

 

[Dick Puller]

Part L is miles behind the times & has lots of contridication.

Most will use the 4 tappings on a 'C' plan.

With SF it's always wise to have some kind of gravity heat dump, regardless of controls.

 

[poolebybirth]

Thanks for helping. So you are allowed to fit a cylinder stat AND a 2port on a semi gravity sold fuel system to hw?? but with the stat closing the 2 port, the excess heat path from the SF boiler to the cylinder may be closed off?

Is it also usual/easier to have 2 header tanks with a semi gravity system and a 4-tapping boiler?

 

[Dick Puller]

You need a heat dump with any SF system, regardless of controls.

 

[poolebybirth]

I understand that, but i just wondered if you could have a cyl stat and 2 port as well...

Also, with a 4 tapping boiler: is it usual to have 2 header tanks (1 for hw and 1 for the HTG side) or just 1 larger header tank with 2 vent pipes and 2 cold feeds?

 

[gas4you]

Although I am not anyway qualified in solid fuel installation, it has always been, as far as I know, that with solid fuel you cannot have any form of cylinder stat and zone valve on the cylinder.

The cylinder is used as a means of taking the heat out of the boiler (the heat sink) as solid fuel boilers cannot instantly respond to the call for heat ending as a gas or oil boiler can.

I stand to be corrected by any resident HEATAS installer on here if needs be

 

[poolebybirth]

I believe you can use a tap stat (like a trv) on the primary return from the cylinder can't you though??

 

[gas4you]

This would still cut the circulation to the HW clinder when it closes though.

Maybe this is why most solid fuel installations also have the bathroom rad on the gravity HW circuit.

 

[Dick Puller]

Solid Fuel appliances need two means of escape, in other words a direct route from the boiler to the F&E tank.............via the F&E.

As said the cylinder is used to take the heat from the boiler, but with most Solid Fuel appliances you also need a heat dump - just in case you have power failure!!

A gravity system is the norm on SF HW F&Rs. Of course all systems worked on gravity only before circulators where introduced into Central Heating systems.

Installation of Solid Fuel appliances is not a DIY job, best get the pros in.

 

[poolebybirth]

2 means of escape? so you mean 2 vent pipes and cold feeds, one directly to the boiler, and 1 tee'd off from the hw flow?

I'm not attempting an solid fuel installation was just trying to get my head around the regs and how the systems work, am just interested really.

is there 2 separate circuits then, ie 1 for the h/w and 1 for the htg ? unlinke with fully pumped systems where the same water heats both the h/w and the htg?


if the cylinder takes the heat, and you say you need a heat dump incase of power failure-what power failure are you talking of here??

 

[Dick Puller]

and you say you need a heat dump incase of power failure-what power failure are you talking of here??.......................Are you trying to have a laff mate???