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New boiler installation question

So I just finished replacing my 18yr old MZ wall hung boiler due to a cracked heat exchanger. I can't complain. In 18 yrs it's the only issue I had. I replaced with a dunkirk DB165. Just fired it up tonight for first time and everything is great except 1 thing. On my old mz boiler my external circ pump was tied into the boiler circ pump so they kicked on simultaneously. After room tstat was satisfied and not calling for heat the pump would continue to run circulating the hot water till it dropped below a certain temp. With this new boiler I had to buy a single zone switching relay so the external circ pump kicks on when room tstat calls for heat but once satisfied and turns off it also turns off the circ pump which now is not circulating that excess hot water like the old system did. How can I get the pump to keep running till water cools down? Appreciate any input you can share. Thanks!


  • hot_rod
    hot_rod Member Posts: 22,244
    Either a time delay relay, or a temperature control to run the pump as a post purge.
    Some boilers have that purge control, did you read through the control section of the manual?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream