Greenstar Boiler with Indirect DHW with Zone valves - many questions

mattmia2

i have concerns with any t-stat that will freeze your pipes if the battery goes dead

fenkel

> @mattmia2 said:
> i have concerns with any t-stat that will freeze your pipes if the battery goes dead

Understand....

fenkel

> @dtlemoine said:
> All - first post here, but long time lurker. Many, many thanks for the pages upon pages of wisdom that I've consumed over the last ~18 months troubleshooting a flaky install of a Mod Con with Indirect DHW.
>
> For some background, I have 5 heating zones plus the indirect DHW. A couple of the heating zones are bordering on micro-sized, but I can see why the original owners did it this way, a couple zones are dedicated for rooms that don't get much use and can be kept pretty chilly in the winter. Perhaps electric would have been a better choice for those rooms... But I digress.
>
> The 5 heating zones are controlled by a Taco ZVC406 Zone Valve Controller and fed by a Taco 007e. The indirect DHW is a Mega Stor 40 gallon, fed by it's own Grundfos 15-58, currently set to high. Boiler is a Bosch/Greenstar KWB42-3. There are no check valves anywhere in the piping. The boiler is plumbed with the LLH removed. Boiler circ is also set to high currently.
>
> Piping layout... Boiler LLH goes to 1" iron supply pipe to a tee for the indirect DHW. 1" iron pipe continues after the tee to the expansion tank & airscoop, changes to 1" copper, followed by Taco 007e, followed by 1" copper manifold with 5 zones of 3/4" copper, each with a ZV. All 5 zones plus the indirect DHW return via 3/4" copper to a 1" copper manifold, eventually changing to 1" iron back to the boiler's LLH.
>
> The indirect is fed by a 3/4" copper to the grundfos circ, and return is also 3/4". The boiler controls the circulators, alternating between space heating and indirect, with indirect on priority at max output, while heating temp is handled by the outdoor reset.
>
> I have a number of questions...
>
> 1) Do I need to swap out the 3/4" piping feeding the indirect DHW with 1"? Mega stor calls for 1", the tank has trouble keeping up with a single shower that isn't pulling more than 2.5 gal/min. The circ on the indirect seems plenty robust. I suspect the 3/4" is having trouble carrying all the BTUs to the Mega stor quickly enough.
>
> 2) I get phantom flow on whatever heating zones are calling, when the indirect kicks in. I can tell as the heating zones will get scalding hot, when the outdoor reset could have been calling for nice gentle heat. I think it's actually flowing backwards through those zones. Is it possible to wire the system in such a way the zone valves close when the system calls for DHW heating, even if the thermostats are calling for heat? If not, would it make sense to add check valves to each zone? We previously had a check valve in the Taco 007e but it was noisy as heck so the plumber removed it. Said not to worry about phantom flow...
>
> 3) I get a crazy amount of cycling. I've back-of-the-envelope calculated my heat loss at around 100k BTUs on design day. The boiler produces 151k BTU, but only has a 4.2:1 turndown so min fire is ~36k BTU. I'm well under 36k most of the year, so the system cycles, I get run times of 1-2 minutes typically, so obviously losing efficiency here. Aside from swapping out the boiler for a smaller unit, with better turndown ratio, is there anything I can do here? Buffer tank? If yes, I have a few more question on sizing and piping...
>
> 4) The installer didn't include an expansion tank for the DHW (cold water supply has a backflow preventer). How critical is the expansion tank? I plan to put one in, but wondering how quickly this needs to happen. He didn't pipe in a heat trap either, I can feel the hot water climbing towards the ceiling when not in use. I'll configure with a heat trap when I cut in to the piping to install the expansion tank...
>
> 5) Bonus question, for any Greenstar owners... Assuming for a moment the thermostats are calling for heat, and DWH is satisfied, the internal boiler circ and Taco 007e will periodically shut off. Like, all of the sudden, system goes silent. Stats are still calling for heat, but everything just shuts off. SyYstem sits silent for 4-5 minutes, then circulators fire right back up and system continues on it's merry way.
>
> Any window folks can provide is extremely appreciated. I've long grown tired of going back and forth with the original installer, and the story above is much improved since the original install, at this point I'm hoping to just be tidying up the loose ends.
>
> Happy to provide more details about the install, clarifications to anything I described poorly, and photos wherever helpful.
>
> Cheers,
> Dave

Dave,
If you still have the temperamental on and off zone pump..
Try this: take the black cover off the pump...next time it shuts down try and get an electrical reading at that contector..
If you have power coming from the boiler, the issues is something past that connection..like the connection or maybe the pump..
Id also do the same test with the connector for the ch pump at the boiler..
If you dont have power coming to it.
You might have a board failure...
I also noticed in the middle of the top of boiler, a dark discoloration, what is that?
Did someone add glue around the intake and exhaust lines?
We had several leak under that setup.. at the upside down "y" pipe going into the top of boiler..
We try and get this y pipe level if possible, but still take precautions
Which possibly could leak water down and inside the boiler... it only takes a couple of drops of water to cause problems...
Fyi: we take white silicone caulk and caulk around the two halves. We also add rubber washers to the gas tester ports. As a precaution measure.
If possible i try and remember to get a few photos.

dtlemoine

Quick update to all - with the tip on the RIB, I was able to get the ZV's to close during DHW calls. I wired the RIB's 120v input to the DHW pump's power on the back of the boiler, and sent the 24v relay to zone 6 (priority) on the Taco controller. Now, when the DHW pump is activated by the boiler, it closes the relay and effectively fools the ZVC to "open zone 6" (there is no ZV on 6, so obviously nothing physically happens here) but the benefit is due to priority, all other ZV's shut. This has reduced the rebound time on the indirect by totally stopping all phantom flow and effectively increasing supply temps to the indirect.

As for the boiler pump (and therefore supply pump, also powered directly by the boiler) periodically shutting down, I noticed this would happen every 8-15 minutes, for a total of 6 minutes at a time. I believe this is the boiler's anti-cycle protection kicking in. What that meant in my scenario however was that I was losing heat for 18-24 minutes per hour!!! I rewired the 120v input for the circulator for the zones to the ZVC. Now, the boiler still goes into anti-cycle (flame and boiler pump shut down) however the system still circulates the hot water to my rads that are calling. Once the supply temp drops enough, the boiler exists it's anti cycle and fires up again.

Definitely more opportunities for tuning, but I am hearing the condensate pumps cycling much more frequently, so I'm thinking I'm getting more runtime in the condensing stages, nudging efficiency up. Fully recognizing that we're well in to shoulder season, so the system temps are down as well, so not necessarily a great apples-to-apples comparison.

fenkel

Turn Off automatic anti-cycle function.. service function 3.A, set this to 00..