Setting different setpoint with Tekmar control

DL

Our boiler seems to cycle on and off more than it should.
The boiler averages an 'ON' time of about 2 minutes each time (this is ok?).

The system is controlled by a Tekmar 363 control.
Is there a way to setup a larger setpoint differential so hopefully the boiler will come on less frequently but stay on longer each time? What is a normal differential to use?

Or, do you have a better suggestion?
We have a Vitogas 050, Tekmar control with outdoor reset, about 8 zones, and an indirect DHW tank.

Thanks

Justin Gavin

First I need some readings

First pull off the cover.
2nd switch the little Lock Dip switch to unlocked
(Make sure when in this mode you do not adjust anything!)
Touch Item until you see View in the upper Left hand corner.
as you hit the arrow button right down all the settings that are there and let me know what they are.

I will let you know from there what you can do.

Good luck.

You can e-mail me if you wish.

Justin

Wayco Wayne_2

Is the

boiler sensor on the Return, or the Supply? WW

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mph

Vitogas 050

If I recall correctly, the system pump on the Vitogas 050 is controlled by an internal aquastat. Unless you've done some rewiring, when the tekmar calls for the system pump, it won't see a rise in supply water temp so it will call for the boiler to fire. Now the system pump will start running. If the boiler was close to set point the tekmar will then shut it down. You'll have short cycling. Make sure the system pump is wired directly to the 363, and not the aquastat in the Vitogas.

This is all from memory. It would be good to call your Viessmann rep to get the straight scoop.

Jeff

DL

First of all, thanks! You guys are great!
I'm just an end user trying to figure things out, not a heating contractor. I'll call in a contractor once I can figure out if something does indeed need fixing.

Justin: I'll write down the Tekmar setting tonight.
WW & MPH: Would a digital photo help?

How do I physically tell if:
1. Boiler sensor is on the return or supply?
2. System pump is wired directly to Tekmar 363?

If out temperature outdoor is about 50 deg F, what would be considered short cycling?
Without any DHW usage going on, our boiler might fire for 2 minutes, shutdown for 5-8 minutes, then come on for another 2 minutes. This is in a well insulated, almost new house.

I suspect my natural gas bill is 20-25% too high for a house that is the same size. And, I have outdoor reset!

Thanks again!

hr

That boiler

has a non adjustable aquastat set to 140 degrees, I believe for boiler return protection. If your tekmar has a minimun boiler protection feature, you may need to wire around the factory one. Best to contact Viessmann for their advice and wiring changes needed.

Unless you are comfortable with changing the boilers internal wiring?

hot rod

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DL

Here are the VIEW settings in the Tekmar 363

DHW: 124 deg F
SETP TRG: - - -
OUTDOOR: 39 deg F
MIX TRG: 108 deg F
MIX SUP: 106 deg F
BOIL TRG: 150 deg F
BOIL SUP: 132 deg F
DHW TRG: - - -

If I'm not mistaken, DHW TRG actually shows a number at some point. I can't remember, maybe it's when the boiler is firing.

Does everything seem fine or can you suggest any fixes?
Thank You

R. Kalia

suggestions

> I suspect my natural gas bill is 20-25%

> too high for a house that is the same size. And,

> I have outdoor reset!


Another homeowner here.

(a) Do you have the manual for your Tekmar? If not you can get it from the Tekmar web pages. It will tell you how to set various things. They also have a separate document somewhere that explains these options. Your box may have an automatic differential option (increases when water temp increases).

(b) Eight zones? A possible reason for short-cycling is that while your furnace may be properly sized for the whole house on the coldest likely day, it is way too big for when only one zone needs heat on a 50-degree day. You need a zone controller that handles the competing needs in a way that reduces short-cycling. (PS while short-cycling is bad, it's probably not going to make a 20-25% difference to the bill, although maybe it could in some situations.)

(c) You 'suspect' your gas bill is too high...I suggest the following. If you have gas bills from summer and winter, for roughly the same one-month period, subtract the two (the summer bill tells you the hot water and dryer and etc use, i.e. non-heat use). Divide the difference by the number of degree-days in the winter billing period (I hope this is printed on your bill). Now divide by the number of square feet in the house. Change therms to BTU: 1 therm = 100,000 BTU. So what do you get in BTU per sq ft per degree-day? An old house may be 10 or even 15; a new house would be 5 or less.

DL

I have the Tekmar installers manual but I don't know enough yet to change any settings. Might mess things up.

One thing that might help figure things out.
On each of my 3 floors I have an electronic thermostat that tells me how long it was 'on' each day. There are other mechanical thermostats in the house too.
Anyway, the one in the basement is only on about 4 hours each day. The one on the main floor is only on maybe 2 hours. The one running the bathrooms upstairs varies from 6 hours to 24 hours. It runs 24 hours when I set it high so I get constant circulation to keep the floors warm.
The bathrooms do not overheat indicating the water temp is probably ok.

However, when the bathroom thermostat was set to only run about 6 hours per day, the boiler was still firing up too often in my opinion. Only my wife and I live in this house now so we are using very little DHW too.

This leads me to think some setpoint differential is too low (for DHW or heating water temp). The boiler seems to fire too often for our usage.

Thanks for any help.

R. Kalia

well, that's part of the problem right there

> On each of my 3 floors I have

> an electronic thermostat that tells me how long

> it was 'on' each day. There are other mechanical

> thermostats in the house too. Anyway, the one in

> the basement is only on about 4 hours each day.

> The one on the main floor is only on maybe 2

> hours.


The whole point of outdoor reset is to have the circulators run [almost] all the time, with heat supply to the zone determined by water temperature rather than by running time. The thermostats should always be calling for heat. In practice this ideal case will not be reached, especially since your different zones have different needs (the thermostats' role is to "police" the zones and cut off the heat only if/when a zone gets too warm). But with a cast iron boiler, the water temperature has to stay above where it might condense, and so you get no benefit from outdoor reset on a 50F day. (The Tekmar has a setting that says "Don't allow the water temperature to get below xx" where xx is maybe 130F. Outdoor reset is not really worth it with a cast-iron boiler, however fancy the boiler brand.

PS Try calculating therms/sf/dd.

hydronicsmike

Chuckles, please explain your statement....

"Outdoor reset is not really worth it with a cast-iron boiler, however fancy the boiler brand".

Why do you feel that way?

DL

Vitogas Internal Aquastat

Mph & HotRod,

I'm finally getting around to checking on my heating system again.

You both mentioned that my Vitogas 050 has an internal aquastat and I might have to wire around it to allow the Tekmar 363 to call for the system pump without firing up the boiler.

I phoned the local Viessmann office and they didn't seem to understand why this would be the case. Maybe I was explaining it incorrectly as I'm a heating newbie.

Can any of you explain it a bit differently so I can run this by Viessmann again. Better yet, is there an easy way for me to verify it myself?

Sounds like what you wrote could very well apply to my setup.

Has anyone else setup a Tekmar control with Viessman Vitogas?

Thanks!

hydronicsmike

Didn't we talk today?

Dan,

MPH and Hot Rod pretty much have it nailed down. Make sure the Boiler Pump runs off the 363. Other than that, keep the Differential set to AUTO. If you got more questions, call or email me.

Thanks,

Mike

ScottMP

Me too

I'd liked to here the explanation for no outdoor reset on a cast iron boiler ?

Scott

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