Gravity primary system to a C Plan...?

[Mike2007]

Is there an problems converting from a gravity primary system to a C Plan?
In order for the house to heat up to a reasonable temperature the DHW is boiling (or nearly).
Suppose it will be 4 tapings on the boiler and will need on more thinking a 2-port zone valve for one the primaries??
What do you think?

 

[chrishutt]

Suppose it will be 4 tapings on the boiler.....and may need...on more thinking a 2-port zone valve??

Would you like to try that again, in English please?

 

[Softus]

You need to cap off one flow and return tapping at the boiler, and there's only one way do it safely for any given boiler - the manufacturer will advise, or see the MIs.

 

[Mike2007]

This is basically what exists, but I want to install a two-channel programmer ans valve to control DHW and CH independently. So the cylinder water does not boil in an attempt to heat the cold house!

This is what I had in mind to have some control over the DHW (found on web!)

 

[ChrisR]

Not as simple as it looks, to do it right.
See honeywell's much better ideas for C plan:
http://content.honeywell.com/uk/homes/Catalogue/Sundial Plans/3.1 C Plan.pdf

You have an issue to deal with one way or another - you have to ensure that the path from the boiler to the vent is direct and not via a pump or valve.
You could alter the plumbing, which can be a swine in some installations.
One way to get out of jail is like this:

So
IF the programmer (not shown) is calling for HW
AND the pipe from the boiler is hot - pipe stat, green
AND the cylinder isn't hot enough - cyl stat, blue
THEN the pump, blue, runs.

I've never needed it but you could add a motorised valve, pink, if you had trouble with gravity circulation. In practice the pump slows that right down. Your stats would open the valve which would start the pump from its auxilliary switch.

You might be tempted to ut the pump in the cold-feed/return between the cylinder Tee and the boiler, but you shouldn't, because the path from the feed tank to the boiler should be unobstructed. Seen it done, though.

 

[Mike2007]

Hi Chris,
I understand what you are saying, but the new pump would encourage DHW heating but have nothing to discourage water heating (which is where I am at).
But surely if there was a zone valve on the return the boiler would only start up when the was a call for water (zone valve also open). The only other boiler start up would be call for heating (CH pump starts as per normal)?
Danfoss-Randall info: http://danfoss-randall.co.uk/pcmpdf/introducing motorised valves.pdf
Honeywell info: http://content.honeywell.com/uk/homes/systems.htm
The Honeywell having a zone valve in the return primary, thus cutting of flow when powered down! Boiler only on if CH calling.

 

[ChrisR]

but have nothing to discourage water heating

As explained, the new pump is sufficient impedance that gravity circulation stops in my experience, though you could add a MV if it wasn't.

Yes you would have to wire it up corrctly, to avoid the problems you mention!

 

[Terrywookfit]

Stick to "C" plan its not fully pumped but who gives a toss!!

 

[D_Hailsham]

I had a gravity HW and pumped CH for years at my last house. Converting it to fully pumped was too expensive so I opted for the C plan (which is designed for this scenario) It does not convert the system to pumped HW.

Suppose it will be 4 tapings on the boiler

But looking at your "what exists" diagram, HW already has separate connections to the boiler from the CH.

Which is correct?

If you already have the HW in separate tappings, then all you need is a 28mm Valve (Honeywell V4043H1106) in the return from the cylinder to the boiler as shown in the diagram at:

http://content.honeywell.com/uk/homes/systems.htm#CPlan

If you look at the wiring diagram, you will see that the pump only runs when the CH is on.

Your wiring diagram for "what I had in mind" is incorrect. The grey lead from the valve has to have a permanent supply not via the time clock. (See the Honeywell wiring diagram)

 

[Terrywookfit]

Your wiring diagram for "what I had in mind" is incorrect. The grey lead from the valve has to have a permanent supply not via the time clock. (See the Honeywell wiring diagram)

Why ???

If the timeswitch is off no supply is required !!

 

[Mike2007]

The grey core does what in the zone valve when its not a switched live?
Thanks for everyones input by the way!

 

[D_Hailsham]

Your wiring diagram for "what I had in mind" is incorrect. The grey lead from the valve has to have a permanent supply not via the time clock. (See the Honeywell wiring diagram)

Why ???

If the timeswitch is off no supply is required !!

The grey core does what in the zone valve when its not a switched live?

You are quite right!

I was just following the Honeywell wiring diagram, see below:

The job of the grey wire is to supply power to the boiler when the HW is calling for heat. The motor is energised via the Cylinder stat and makes the contact between grey and orange. Now, obviously this can only happen when the HW is on at the time switch, so the grey could just as easily be connected to terminal 6 on the junction strip!

Why Honeywell recommend connecting grey to an permanent live is a mystery. They do exactly the same in the S plan wiring.

Can anyone explain Honeywell's thinking?

 

[Mike2007]

So that last diagram, heating is on by itself, valve is closed??

 

[Terrywookfit]

So that last diagram, heating is on by itself, valve is closed??

Yes that is correct !

 

[D_Hailsham]

So that last diagram, heating is on by itself, valve is closed??

Yes that is correct !

Just make sure you buy the correct valve!

You need the V4043H1106 for 28mm gravity feed or the V4043H1056 for 22mm gravity feed