wiring help needed

[ir50]

Hi, Im trying to workout how to wire up 3 way motorized valve. I have a system boiler that i have effectively converted to a combi using a plate heat exchanger. The 2 issues are, the boiler can only be controlled via the room stat connection so effectively a short across the 2 terminals, rather than a positive control feed. Second issue is the hot water uses a flow switch to trigger demand rather than using a tank stat as would normally be the case. I have a relay I can use which has 2 sets of contacts but just can't work out how to wire it all up. Can anyone offer a diagram. Thanks

 

[matt1e]

possibly what are you trying to achieve?
how are you planning on controlling the temp of the DHW btw?
a schematic would be useful
Matt

 

[stem]

Diagram below.

Flow switch connected to live supply, so operates whenever hot water is required. The motorised valve is not powered so rests at hot water position. The relay is energised to provide potential free contact for boiler.

The flow switch also supplies 'live' to central heating via programmer to turn off central heating when hot water is required (Note if flow switch doesn't have changeover contact a second relay could be used)

When central heating is required, the room stat provides a live to grey (hot water not required) and white (central heating required) this winds the valve to central heating only position, the orange wire is then energised operates relay and fires up boiler.

Untitled

• stem
• 4 Feb 2013
• 1

 

[dcawkwell]

The simpliest wiring would be flow switch to grey and white.
So when water is demanded the valve moves. I would wire directly from the flow switch to the boiler so that the boiler is starting to fire up as the valve is moving across.

The central heating will work just as normal thermostat switches boiler on.

You are using the central heating connection on the 3 way valve for hot water and the hot water connection for the central heating.

The boiler will not be able to control the hot water temperatue so I would use a thermostatic valve to set this.

 

[stem]

dcawkwell's idea is slightly simpler as it means the flow switch doesn't need to have a changeover contact, however, you will have to reverse the plumbing connections to your 3 port valve as the HW port will need to go to the heating circuit and vice versa. The changeover to the hot water position will take a few seconds longer, as it is motor driven there rather than being pulled by a spring. Although I doubt that would be crucial. A revised diagram is below:

I would wire directly from the flow switch to the boiler

I don't think you could do this because then the valve would move to the hot water position when either the room stat or the flow switch call for heat, the orange wire from the motorised valve microswitch will provide the isolation

Untitled

• stem
• 4 Feb 2013
• 1

 

[ir50]

Thanks for replies guys.

Stem - think the fact that flow switch doesn't have a changeover connection is what's been stumping me. Thanks for diagram.

Dcawkwell - will look into that and make a diagram first.

Matt1e - just trying to control both dhw and ch using 3 port valve. This valve might have been the wrong choice...prob should have got a diverter instead.

I already have dhw to the taps controlled via a mixer

As another thought i was wondering if i could use smart pumps instead of valve in an s plus plan. As i have these already and ideally need to split ch into 2.

 

[dcawkwell]

dcawkwell's idea is slightly simpler as it means the flow switch doesn't need to have a changeover contact, however, you will have to reverse the plumbing connections to your 3 port valve as the HW port will need to go to the heating circuit and vice versa. The changeover to the hot water position will take a few seconds longer, as it is motor driven there rather than being pulled by a spring. Although I doubt that would be crucial. A revised diagram is below:

I would wire directly from the flow switch to the boiler

I don't think you could do this because then the valve would move to the hot water position when either the room stat or the flow switch call for heat, the orange wire from the motorised valve microswitch will provide the isolation

Untitled

• stem
• 4 Feb 2013
• 1

Yes I'd have to use the orange wire for the hot water. Pity. As that would
have got the water working faster.

 

[doitall]

Why not have an S plan

 

[stem]

Why not have an S plan

Primarily because the system would need to select either hot water, or central heating (not both at the same time) and give hot water exclusive priority. That would mean with a S plan, that when the hot water flow switch was operated, the central heating valve would have to close even if the central heating thermostat was calling for heat.

The three port valve is simpler because it can be wired without using the mid position, so that it closes off the heating port when hot water is required.

 

[doitall]

Or you could use changover relay and have hot water priority.

 

[ir50]

Will be trying stems second diagram shortly.
My relay is a changeover with 2 sets of contacts so would be interested in s plan option for a later enhancement particularly if i can use pumps instead of valves....can i?

 

[stem]

You can use a relay with changeover contacts to switch two '2 port motorised valves', but this can't be the same relay that you are using to provide the potential free contacts for the boiler, you will have to get another one.

 

[picasso]

How many kilowatts is your boiler output ?

 

[Whitespirit66]

If the OP wants some inspiration, here's a video from a well known haggis-muncher of these boards - Mr Dick Puller.

http://youtu.be/Ft5fsHQy-Wg

Judging by some of the marks on the walls, it must have been Burns night.

 

[DP]

Picasso, I was about to ask the same question.