Burnham Revolution & Tekmar 420: ping-pong!

Chris N

Thanks for the suggestion, Glenn. I'll give it a shot.

Question: any specific requirements on wire type that runs into the jacket?

Question: What if anything should I watch out for? Just improved cycling?

This has been extremely helpful.

-Chris

Chris N

Greetings. I recently finished adding some Tekmar controls to my Burnham Revolution. I've got the 420 ODR with a 336 zone manager for two circulator-zoned zones and a couple Tn4 networked thermostats.

The 420 is just connected to the T-T connection on the Revolution aquastat; the 420 is set for a minumum temp. of 85deg, design 160deg and max of 180. Aquastat is unmodified at 210deg. Everything works quite well and I get near-constant circulation on the downstairs zone.

The trouble I'm having is as follows:

1. Downstairs zone on, up to temp; target ~130deg
2. Boiler not running, but hot; ~170deg.
3. Cold upstairs zone kicks on
4. Supply temp. drops fast due to cold water from upstairs
5. 420 kicks on the boiler
6. Since it's hot, the internal boiler pump comes on @ high
7. Supply temp. shoots up fast
8. 420 kills boiler as we hit the top of the differential
9. Internal pump stops, no more heat output; supply drops

And we oscillate around steps 4 -> 9 approximately every 30sec-1minute. Since the boiler is under 180 the poor burner keeps trying to light, too, but often doesn't make it before the 420 kills everything.

Any suggestions on tweaks to the 420 configuration which might help? Given the internal primary/secondary, I was suspicious something like this might happen. I'm tempted to try powering the VS3000 from the 420's pump terminals rather than the aquastat-- that way it would "always" run and the boiler output would ramp up and down more slowly....

Comments?

Josh_10

Have never installed one of these boilers but I think it uses the same control system as both the TT Prestige and the Weil-Mclain Ultra. Both have a 0-10V remote direct drive interface that can be installed so that the Tekmar actually drives the modulation rate. This will prevent the short cycling and the "ping pong effect". See if an interface is available! Usually they are less than 200 bones.

Unknown

Chris

Since you are not using a "System Pump" you could certainly try wiring the VS-3000 to the System Pump Terminals instead of powering it from the L8148E Limit control. I've never heard of this being done so it would strictly be experimental. I don't see a setting to control the System Pump contacts on this control based on using Zone Pumps or Zone Valves so I am assuming it will function regardless of type of zoning. I would also try increasing the Boiler Delay time a bit to allow the Internal Pump to utilize the leftover temperature in the boiler.

We normally advise using a two-stage staging control to handle the Revolution in reset applications. We would use Stage 1 to control the VS-3000 through an isolation relay and Stage 2 to fire the burner through the normal T-T connections. While what you are going to try is similar, it will be different but is certainly worth a try. Let me know how this works as I would like to know for future applications as the TN4 controls are beginning to grow in popularity.

As far as the VS-3000 control being similar to other manufacturers 0-10v DC Modulating Controls as stated in one of the responding posts, they are not at all similar. They are a variable speed pump control and not a modulation control. Hope this helps.


Glenn Stanton

Manager of Technical Development

Burnham Hydronics

U.S. Boiler Co., Inc.

Chris N

Thanks for your reply, Glenn.

I've got some additional information this morning. The problem doesn't look to be related so much to the 1st/2nd zones as it is to trying to maintain a particular target temp.

I have the 420 set to automatically select the boiler differential.

During morning recovery, the 420 has been targeting 145deg for the supply temp. After a cycle or two, the boiler is hot (>= 170deg). It looks like the 420 uses a differential of about 10-12deg. So boiler gets kicked on at 140deg, I get a blast of hot water since the VS3000 goes to high speed, and the supply temp. hits ~150deg. in about 30 seconds, at which point the 420 kills the boiler.

It appears as if the 420 "learns" from that mistake, because on the next cycle it uses a much larger differential and lets the supply ride up to ~165deg before shutting down. It does not, however, seem to "remember" that for long since after a while it tries tighening the differential again.

Question: Would I be better off with a manually set differential?

I've got two options for powering the VS3000: the 420 has a "primary pump" contact for running a line-voltage circulator. This can be configured to run for any call-for-heat.

The second option is that the 336 zone manager (which I'm using to run the two zone pumps) has a "zone group pump" contact for line-voltage circulators. This can also be configured to run on any call-for-heat.

The main distinction is that the contact in the 336 is configured via DIP switches on the board, where as the contact on the 420 can actually be configured at each thermostat.

My primary concern about re-wiring the VS3000 was not knowing if that was "safe" to meddle with the boiler internals in that way. It sounds like the two-stage setups you describe are similar, so that makes me feel a lot more comfortable about trying that.

I guess the only difference in my case is that the VS3000 will run continuously. As a result, the boiler will see more cold starts, I guess.

Question: Anything in particular I should watch out for when trying this?

Thanks again!


-Chris

Unknown

Chris

Are you using an Indirect Water Heater? If you are this will complicate wiring a bit since Indirects are usually set up to prioritize their flow and heat call. Let me know the answer to this then I will be able to decide which way is best.

Glenn Stanton

Manager of Technical Development

Burnham Hydronics

U.S. Boiler Co., Inc.

Chris N

Hi Glenn. I do not currently have DHW running off the Revolution. (I might in the future, but not now.)

Now that you point this out, I think that it probably makes sense to run the VS3000 of the 420's "primary pump" contact since its the 420 that would see any DHW demand and I'd need the VS3000 running for DHW too...

-Chris

Unknown

Chris

If you don't have an Indirect then there is no concern about the System Pump Terminals of the 420 getting interrupted on a DHW Priority demand for now. Here is how I would do it.

Disconnect the wires from Terminals #1 and #2 of the VS3000 and cap them off. Wire Terminal #1 of the VS3000 to Terminal #68 of the 420 Control and Terminal #2 of the VS3000 to Terminal #69. You can also increase the Boiler Delay time in gradual increments until it performs like you would want it to. If you delay it too long though, the water may cool down enough to cause the Internal Pump to slow down. The boiler has internal protection for return water as low as 55°F so that isn't a concern.

Glenn Stanton

Manager of Technical Development

Burnham Hydronics

U.S. Boiler Co., Inc.

Jay_14

cycling

Hello Chris,

Recommend contacting tekmar as they manufacture both the 420 and the VS3000. Interaction of the cycling between mixing controls and boilers controls is a known issue and there are solutions in dealing with it.

Jay