Reduced Temp Mode on Vitotens

Mike T., Swampeast MO

Has anyone tried this on a fully TRVd gravity conversion without low-loss header and using only the internal boiler pump?

I've been reluctant figuring that if all the TRVs get starved that the little circulator would start short-circuiting through the big, low, close TRVs.

This morning I turned up two large, deeply set back (about 12°) rads with 170 sq.ft. EDR. Within the time it took to read one story in Dan's book "Working" (and wipe/wash), both rads were fully heated from side-to-side! Circulator was still likely below 50% rotation speed!

I was a touch concerned with recovery from setback believing it MUST be adversely affected compared to the more than double sized W/M boiler and B&G 100 circulator. Recovery was always quick for a hydronic system, but this is a true shocker as it seems even faster!

Image shows the point where I turned up the TRVs. (Red = supply, blue = return, grey = flue). TRVs were returned to deep setback level after about 10 minutes.

Mike T., Swampeast MO

Truly Amazing Operation

Just did another little experiment.

Clocked boiler for five cubic feet--it's been in full modulating mode for many hours. Input was right at 26 mbh/hr or just a hair above the lowest possible modulation level.

Turned up TRV on one huge rad with some setback (about 7°). Not "cranked" mind you--just from a setting of "1" to the little red triangle. When I turned up, the radiator wasn't even warm to the hand, but supply line to it was hot, so I know it was circulating a small amount of water.

Rushed outside and watched meter. I could see the speed increase and after 30 seconds, clocked it for the use of one cubic foot. It took 1 minute, 22 seconds or about 44 mbh. Went back inside immediately--rad was now completely warm from side-to-side but not quite as hot as the supply pipe. Turned TRV back down to the previous level.

Rushed back outside and I could see the speed of the meter decrease and after 30 seconds, clocked it again for one cubic foot. 2 minutes, 10 seconds or about 27 mbh!

This boiler IS learning to use those big main pipes as a buffer and to control that buffer with almost uncanny precision!

With the old W/M, the boiler would fire almost immediately if you raised a TRV, but it lacked the control ability to know how much additional heat to add and the "smarts" to know when to stop adding heat.

Ted_5

Hay, Mike it is still learning

and it will continue to learn how your system works. I noticed a big change in the amount of cycles in my boiler after one heating season. Sounds like you are having fun!

Ted
Viessmann rep.

Mike T., Swampeast MO

I got sidetracked in this post, but any experience with reduced temperature mode on a converted gravity system without low-loss header and TRVs on all rads?