Problems with Tekmar Mixing Station 704

bm2005

We had radiant heat installed 3 years ago in part of our house. It uses Tekmar Mixing Station 704.  There is an oil boiler that heats water for the radiant heat system and for the rest of the house that uses hot water baseboards.



There haven't been any issues with the radiant heat until a couple of weeks ago. We started noticing that after a sharp temperature drop outside the Tekmar device would not start the circulator pump for a very long time (5-10 hours). There would be demand for heat from all zones and the rooms would get colder and colder  but the pump would stay off. Eventually, the pump would start and the system would be back to normal for a while. Then it would stop working again. There seems to be a bit of a pattern - it is mostly off at night and mostly works during the day.



We had technicians look at it but both times they came over everything was functioning ok and they said everything seemed fine.



I would appreciate any ideas/speculation about what may be going on. Thanks.

NRT_Rob

haven't used one

but I believe it should show what injection percentage it is attempting to provide at any given time.



when it's not running the pump, is it indicating that it's TRYING to provide a high injection rate, or is it acting like there is no demand at all?

bm2005

Large difference between boiler and supply mix temperature

Thanks for the feedback. I cannot see any indication of an injection rate.



However, I noticed over the last day that when it stops working, there is a high differential between the boiler temperature (around 190) and the supply mix temperature of the radiant heat (around 120). The Tekmar manual says that it may limit the output of the variable speed injection pump in order to reduce the amount of cool water returned to the boiler and avoid a thermal shock.

Presumably the boiler water is so hot because of the hot water baseboard systems we have in the rest of the house.  When the boiler temperature is lower (~160-170) the radiant system seems to work.



Is it normal that the boiler maintains high temperature for long hours? Is there some tuning required?

How is such temperature differential supposed to be handled to avoid having the radiant heat offline for prolonged periods of time? Thanks.

NRT_Rob

could be cause and effect

if the mixing station is not injecting heat, but it IS passing a heat demand, then the boiler would go up to its high limit temperature. it is passing a heat demand through if it has the hair dryer looking icon up. it is acknowledging a demand if it says "dem" in the lower right hand corner.



if it's not acknowledging the demand, that's the problem.



injection percent is in the lower left corner of the display.



boiler protection should only be active for very low boiler temps.

bm2005

Only temperature indicator is on when not working

The hairdryer looking icon is off. The % sign is off. The DEM icon is off as well. It is not acknowledging the demand even though all the lights on the ZVC 404 zone valve control are on.

I have seen the DEM and % icons on only when is pump icon  (triangle in a circle) is on.



Does this point to an electronic problem with the Tekmar unit? Why would it be acknowledging the demand only sporadically?

NRT_Rob

could be

wiring between the relay and the unit, or a problem with the unit or relay themselves.



You'd have to be able to test for voltage and such to narrow that down further I believe.