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LAARS EBP combo boiler, should be an easy fix, checked everything, ???

CSCS Member Posts: 7
I have a 2004 LAARS EBP combo boiler. I had issues in the past with DHW. I replaced the flow switch maybe 5 years ago with a paddle style switch from the vendor that supplies the external upgrade flow switch. Mine is still internal to the cabinet. It has worked fine for years now.

A month or so ago i noticed our DHW was a little flaky and then it was just gone. By jumpering the leads from the switch we had DHW, although still lowish temp.

Turns out the mixing valve was busted (some plastic parts broke, some o-rings shot) so I replaced the mixing valve internals. DHW is now pretty good but still need to use jumper.

Called the flow switch vendor and he sent me the internals for a new switch. When I removed the old FS it seemed fine (continuity upon movement) but I replaced it anyway. I also checked the inside of the body of the FS (in case obstruction present) and found nothing.

So we have DHW now, but only via jumpering. I am not totally sure that we have DHW to the same degree as when everything was working well. I either have the mixing valve set a little lower or the heat exchanger is not keeping up. However we get hot water and the family is not complaining, besides taking the jumper on and off every shower.

Finally decided to take out the whole FS and check for obstruction that way. Everything looks good and I can both lightly use a pencil and lightly blow to get the paddle to give continuity. ??????

I thought the only other thing it could be is that the heat exchanger is working but partially blocked so that there is enough flow to get DHW but not enough to trigger the FS. The fittings are a pain to get to so I loosened the front DHW side of the plate exchanger and turned the tube enough to blow into it and it flows easily.

WTF!!!????!!! The FS is in the right direction (flow input to the heat exchanger is in the front so my FS is oriented so it points to the front to go to the front fitting).

I live in the southwest, but have a water softener, so I really think things should be pretty clean. The inside of the FS is just black oxide, not scaly.



  • CSCS Member Posts: 7
    guru needed

    I talked to Laars again for 10-15 mins. He said I have checked everything, if I have DWH when I use a jumper and if I have continuity when I actuate the flow switch (taking the whole body out and checking at the PCB) then it should work. I put it all back together and whenever I open the hot water faucet I get nothing on the multimeter. ??? I double checked (for the hundredth time) that I have the switch going the right way. Does not seem possible. The switch actuates very easily with my breath.
  • PlumdogPlumdog Member Posts: 873
    Check the orifice

    I think you have an orifice on the incoming cold to throttle down the flow so it has time to heat the water as it passes thru the exchanger. Try turning on all the hot valves in the house at one time. Is the flow diminished from what it once was? Use your hands to feel the pipes going in an out of the exchanger. Be careful! Should be extremely hot to and from the boiler, cold in and hot out on the domestic side. The by-pass valve should completely block heat from going to the heating side, and the system pump should stop. The orifice is surprisingly small in diameter, and it could have debris lodged. Good luck! 
  • PlumdogPlumdog Member Posts: 873
    Something else.....

    There may be a mixing device to limit the outgoing temp to a safe level, normally cold in one port, hot in one port, and tempered out third. If all your flow is restricted, maybe that device is stuck or clogged.
  • CSCS Member Posts: 7
    mixing valve fine

    Thanks for the reply. I still have hot water, plenty for a shower, and the mixing valve I just rebuilt and should be working fine.
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