I've got following setup for heating water:

  • boiler
  • solar panel on the roof

The overall setup is simple - the cold water enters the system and goes first through the solar panel and then through the boiler reservoir.

Then, as a last piece there is a hot-water recirculation pump (Wilo Star Z25/2) that creates a circuit in between the cold water supply and hot water out.

However, I do not get any hot water out of the taps, despite the boiler working and pipe leaving out of it being hot.

After very long figuring-out and trying to feel where the hot water goes by feeling all the pipework, it seems like if the water was going through pump in the other direction! There also seems to be a check/no return valve installed on the intake side of the pump.

I am very sorry for the rough description - I do not have access to the plans so I've "reverse engineered" the above.

My total uneducated guess is that the shut-off valve is faulty and allows the cold water back into the circulation.

Also, the pump seems to be broken as well (I believe it has been for a while) - what happens when it breaks? Does it normally allow flow through in the other direction even if not broken?


I've drafted the schema of the system: system schem

  • Did the system used to work okay? Has some work been done since it used to work?
    – wallyk
    Commented Jul 19, 2014 at 0:26
  • When you say "I do not get any hot water out of the taps", do you get cold water instead, or nothing at all?
    – wallyk
    Commented Jul 19, 2014 at 0:27
  • I get cold water instead. No work done, just started exhibiting this behaviour
    – petr
    Commented Jul 19, 2014 at 1:04

1 Answer 1


If the hot water is hooked up to your faucets, then hot water should eventually come out regardless of the re-circulation stuff. That is, unless the check valve is the wrong way or the pump isn't letting water flow. Then you would just get cold water.

EDIT I see from your comment that the system was previously working and no work has been done. The check valve must be installed in the correct direction. I don't know your entire system, so, it's difficult to know what's wrong. It seems like there would need to be a check valve between the hot and cold line at last faucet in the plumbing run. Then water from the cold side wouldn't be allowed to come out the hot side in case of a restriction in the hot side.

EDIT 2 Thanks for the drawing. I thought you had a recirc pump so that hot water was always instantly available at the outlets. I think the check valve would be better placed on the output of the pump, but I don't think that's why it stopped working. Although I don't know the likelihood, the problem could be a failed check valve. I don't see how else you could get cold water bypassing the heaters after previously working.

  • Thank you very much! I've added more info - the recirculation is not between the taps, it circulates through the solar panel/boiler (as the boiler is usually off for summer)
    – petr
    Commented Jul 19, 2014 at 10:47
  • It was the failed check valve indeed!
    – petr
    Commented Nov 5, 2014 at 13:03

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