Tekmar 260 (DHW zone valve)

vciecierski

I just installed the Tekmar 260 ODR boiler controller. Everything works as intended except for one little thing…
When there is a call for heat for the DHW, Tekmar receives the call, turns on the pump/circulator, and then opens the DHW zone valve.
Does anyone know why it is done in this order instead of opening the zone valve first and then starting the pump/circulator? It doesn’t make sense to me for the pump/circulator to run when all of the zone valves are closed for a minute or two before they open…

Thank you for any feedback on this!

hot_rod

The tekmar could open the zone valve and the end switch on the zone valve starts the pump

Depending on what zone valve you have it should start opening right away and maybe 30- 40 seconds to full open. That shouldn’t be a problem for a small wet rotor circ.

vciecierski

I am thinking of wiring it so that the heat demand for DHW will come from the end switch on the valve instead of the DHW aquastat. Can you think of any problems this could potentially cause since it is not entirely per the manual?
I still don't understand why Tekmar's sequence of operation is like this. Why would it start the pump when the valve is closed? I can hear the circulator "struggle" before the valve is opened all the way. And it takes about 90 seconds for it to fully open.

Thank you for your reply!

Cucumberer

What terminals do you have the DHW pump and DHW zone valve connected to? I took a quick look at the installation options for that control looks like it only has terminals for looking up either the pump or the zone valve but not both. 

If you by chance have the DHW pump connected to terminals 7 and 8 , and the zone valve connected to terminals 9 and 10, then that sequence of operation makes sense, as terminals seven and eight are for a primary pump connection and when there is a call for heat on the control, The primary pump will turn on first and circulate for a minute or two before the relay at 9 and 10 gets engaged. 

Not sure if that is your set up but that’s the only thing I can see that could possibly cause that scenario with the sequence of operation

hot_rod

You have a pump and zone valve on the indirect? How is it piped?

vciecierski

There is only one pump/circulator for the whole system (on the supply side). 3 zone valves on the return side (one of the 3 is for the DHW).

Pic attached for reference (ignore any and all wiring - this pic was taken before installing the 260).

Cucumberer

That sequence of operation for the control makes sense then. You would either need a pressure bypass on the piping system or you could as you suggested, wire the zone valve motor through the aquastat and wire the end switches from the zone valve to the demand terminals for DHW on the 260. Might not show that wiring option on the applications section of the manual, but i have it on good standing from our local Tekmar rep here that its not a problem. 

vciecierski

Thank you for your reply. Now that I think about this... Wouldn't wiring it through the end switches cause problems with the DHW "post purge" operation? Tekmar would run the pump (for up to 4 minutes) but the valve would be closed at that point... I guess I am back at my original question... How bad is it for the pump to run with all valves closed for up to 4 minutes? The pump sounds like it's working a lot harder but does it really matter?

Thank you again!

hot_rod

Deadheading a circ for a few seconds as the valve starts to open is different then running for minutes at that condition.

Although I seen circulators spend their entire life in a deadheaded condition. Years in some cases.

Maybe a delta p circulator would better handle closed valve conditions. It should ramp down against a closed valve, although not post purging.

There must be a workaround, this can’t be the first time this has come up

vciecierski

I just wanted to say thank you to the forum members and everyone who helped me with this project. This is truly an amazing community.

I ended up installing the Tekmar 260 all by myself (thanks to this forum) and could not be any prouder of myself. Thank you again!

Finished result: