Discuss AND gate for S-Plan DHW priority in the Central Heating Systems area at ElectriciansForums.net

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Does anyone make a 230V AND gate: two mains inputs and which only outputs (2A max, say) when both line inputs are live? I have an S-plan system with two DHW cylinders and need mains output when the heat demand from both ceases (i.e. when both cylinder stats are in the ‘satisfied’ state).
This would be used to tell a weather-compensated boiler that it was OK to drop the flow temperature if the outdoor sensor said so.
 

Leesparkykent

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Does anyone make a 230V AND gate: two mains inputs and which only outputs (2A max, say) when both line inputs are live? I have an S-plan system with two DHW cylinders and need mains output when the heat demand from both ceases (i.e. when both cylinder stats are in the ‘satisfied’ state).
This would be used to tell a weather-compensated boiler that it was OK to drop the flow temperature if the outdoor sensor said so.
Why not just use the satisfied terminal on the cylinder thermostat?
 

Wilko

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If I’ve understood correctly, it may need a relay. One sat fires the relay and the other sat is on n/o terminal :) .
 
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Yes - it needs a relay or equivalent because live output is needed when both stats are satisfied and not just one. Otherwise the unsatisfied (still demanding) cylinder could be heated to less than its set-point in the summer when the W/C ramped down the flow temperature sufficient for the CH but not DHW.
 

sam400

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Hi sounds like an interesting project!

Use each tank stat to pull in a relay.
Then you can link your signal wire thru a NC contact on each relay. (in series)
You can use your NO contacts for the hot water control.
 
T

Toneyz

Hi sounds like an interesting project!

Use each tank stat to pull in a relay.
Then you can link your signal wire thru a NC contact on each relay. (in series)
You can use your NO contacts for the hot water control.
This is the only way I can see it working.
 

davesparks

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You only need one relay.
Connect the orange of both dhw valves to the coil (I assume there is a valve for each cylinder)
Live to the common, N/O fires the boiler and N/C signals the the weather comp.
 

PEG

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It sounded like one cylinder would still be receiving input,until the last to be satisfied,signalled it was.
We may need more description of the system set-up.
 

davesparks

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It sounded like one cylinder would still be receiving input,until the last to be satisfied,signalled it was.
We may need more description of the system set-up.
Yes, with two cylinders there is normally two motorised valves.
The OP needs a signal when neither valve is calling for heat,
 

sam400

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You only need one relay.
Connect the orange of both dhw valves to the coil (I assume there is a valve for each cylinder)
Live to the common, N/O fires the boiler and N/C signals the the weather comp.
That is OR Logic op is looking for AND I think?
 

davesparks

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That is OR Logic op is looking for AND I think?
Yes it is Or logic and the OP mentions And logic, but it achieves the same result that the OP requires in a less complicated manner than they were trying to achieve it.
 
Is it a bit like Power from one source (if present)
is only switched, passed thru ON if single relay is also(AND) energised to pass it ( But things can go wrong is N/C contacts are used for anything )
 

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