Help with pump relay logic for CH change.

[rick]

Hoping someone can spot something simple. I have 2 pumps, that I never want to operate at the same time. In the link I have attached a drawing of my thoughts ?

Condition 1. Programmer in Timed=OFF No live to Heating Ctl board, and no power to pump BP. If flow switch operates, then RLY (after time T) will operate and put power onto pump SP via connection (2b) ? all fine

Condition 2. Programmer in Timed=ON Provides live to heating controller ? and in the event of it calling for heat will provide a switched live feed from ?pump ? and I can use that to power the boiler pump BP, via RLY connection (1a) There are a number of thermostats, zone valves etc. all under control of Heating Control board so can only run pump BP when there is a 'Pump' live signal.

If the flow switch operates when boiler is making a heat call, I need pump SP not to operate, as there would be no power to (2b) that requirement is met

The issue I have is if there is no call for heat and flow switch operates I need pump SP to run ? so I need to get live feed to it at that point ??? currently stumped. Am I missing something that I can achieve given the DPDT contacts in relay and SPDT in the programmer. Otherwise I will have to add in another RLY

Ideas welcome.

[rick]

No ... I have added a shunt pump to an existing boiler primary ....... initially just shut off boiler control .. now rewiring so I can put this via a time switch.

The link below shows original system, and what I am in process of changing it to .... changes to left of store now in place.

Once relay Q sorted ... will then add the thermostatic mixing valve on underfloor heating loop. Evolution of my system. :-)

[rick]

error spotted ... updated diag (blue link added)

same Q on logic though

[Tim Watts]

RLY1b can go to permanent live - the logic remains unchanged. In fact you need that as your flow switch may not be rated to handle the pump.

A CH pump typically takes upto 0.5A with a starting current ten times that. It's the starting current that kills components.

The rest I'm still looking at.

[rick]

(ignore that update - flawed logic) use original link