Boiler not getting heat call. Transformer??

CBRob

Munchkin boiler it's not getting central heat calls but is firing up for domestic hot water.
I believe the problem is a faulty 24-volt transformer. The tekmar 356 unit was flashing on intermittently, and it would initiate a circulation pump intermittently. The mixing pump is part of a bizarre little secondary Loop feeding all of the heat zones from a a little 1/2 inch copper Loop
The pulsing power supply was kind of weird, not sure if that's typical of a failing Transformer.
I checked the low-voltage wires at the top of the Transformer and one can lose quite easily, after reattaching the low voltage wire the Transformer quit working altogether.
I made a youtube video of the pulsing 24v out put
https://youtu.be/avBUQx8QiJg

Jamie Hall

How did you reattach that wire? Generally one can't reattach a wire without a connector or solder or somesuch and expect any kind of good connection. So... it's probably gone.

What else does the transformer power, if anything?

Zman

The 356 is an injection mixing controller. The flashing screen does make you think it is a bad transformer or loose connection. Do you have a multimeter? I wonder why you need injection mixing with a munchkin. It does outdoor reset with onboard controls.

CBRob

> @Jamie Hall said:
> How did you reattach that wire? Generally one can't reattach a wire without a connector or solder or somesuch and expect any kind of good connection. So... it's probably gone.
>
> What else does the transformer power, if anything?

There was just a screw to tighten over the wire, no connectors.
The one transformer powers another tekmar snow control a couple of tekmar relays and all the zone valves.
You can see the little screws in the picture.

CBRob

> @Zman said:
> The 356 is an injection mixing controller. The flashing screen does make you think it is a bad transformer or loose connection. Do you have a multimeter? I wonder why you need injection mixing with a munchkin. It does outdoor reset with onboard controls.

Thanks Zman

Maybe maxing out the 75va transformer with so many valves and relays.

HomerJSmith

The Munchkin space heating is thru the grey TT wires to the thermostats or to a dry switch in a controller and they are together in your video. You might want to reconnect them.

Domestic hot water pump has separate leads to the main board and is controlled by a sensor or aquastat that connects to the main board. The only thing SH and DHW have in common is the priority of the DHW over SH which is set in the programing.

Transformers (class 2 ) have a fuse wire on the secondary. They either work or they don't work. They are not intermittent. Intermittence would be caused by a loose connection in the primary circuit or secondary circuit.

I don't see a view of your whole sys. You're using Honeywell zone valves which draw 7.2 VA each, as I recall, so, a 75 VA transformer is probably more than adequate for the zone valves. The 2 Tekmar relays are drawing probably about 2 amps each or 48 VA each. You can check their rating. Where do they get their power? Burnt points on a relay can cause intermittent power distribution.

I don't know you're sys layout, but a stuck thermostatic mixing valve could cause you're heat pulsations.

Zman

He has 10 zone valves at 8 va. The 003's pull 2.3 va each. The 356 pulls 3 va. All in that makes 87.6 va which is a little much for a 75va transformer.

CBRob

I think the transformer failure was on me...
I had to slide a screwdriver behind a copper pipe to tighten the wire down and I bet I shorted it out.
It was the kind without a fuse or breaker.

I replaced it with another Honeywell transformer, with a breaker.
I have a new tekmar control on the way from supplyhouse.

rick in Alaska

That weird piping is just a conventional injection mixing loop. Most likely if the control isn't causing it to cycle up and down because of the power issue, it is because the small line going back to the main line needs to be throttled back to increase resistance to the pump. That half inch loop only pumps water from the primary loop, into the secondary loop, and then back into the primary loop. It is usually only needs to be moving a couple of gpm, so the line can be 1/2 inch. However, the pump wants to move quite a bit more than that. The Tekmar throttles the pump up and down to maintain a certain temperature in the secondary loop, but if the injection pump is moving too much water, which also moves more heat, the control will turn the pump speed down to try and slow it down to match the output temperature needed. Ideally you would want a flow control on the small line going back to the primary loop that you can throttle back to put some resistance on the pump. This will help the control keep the pump running with just enough speed to keep the heat at the right temperature needed for the secondary loop without overshooting.
Long winded explanation, and coffee hasn't quite kicked in yet, so I hope this is understandable.
Rick

HomerJSmith

Lesson learned--cut the power before making electrical connections. Of course, I have taken shortcuts much to my dismay.

CBRob

> @HomerJSmith said:
> Lesson learned--cut the power before making electrical connections. Of course, I have taken shortcuts much to my dismay.

Yep...
The switch was about a foot away from the transformer.

rick in Alaska

HomerJSmith said:

Lesson learned--cut the power before making electrical connections. Of course, I have taken shortcuts much to my dismay.

True on that one. I just took a Tekmar 537 wire off to make sure it wasn't the problem, and when I went to put the wires back on, one of them touched the circuit board and smoked it. Cost me 125 for a new stat.
I turned the power off before installing the new one.
Rick

CBRob

Rick.
Thanks for the breakdown of the injection pump.

I've been looking at lots of hydronic diagrams lately and had not seen this.

This system of injecting low volume of very hot water into the radiant loop seems counter to the theory of using the latent heat in a condensing boiler.

Is this layout used much any more?

As I see how it operates after replacing the tekmar I might hit you up again on how to improve the injection loop.

CBRob

I might be wrong to assume that the munchkin boiler is condensing...
It has PVC venting and a condensate drain

I found a hole left over from a flue gas probe.

HomerJSmith

That ain't the way to close a CO test hole. Drill a hole for a 1/4" CPVC plug and tap it with a 1/4" pipe tap. Install the CPVC plug.

https://www.supplyhouse.com/sh/control/search/~SEARCH_STRING=1/4" cpvc schedule 80 plugs

rick in Alaska

I am not up on the Munchkin, but if it is condensing, you should be able to pipe it direct without the injection loop. However, it might be piped so that it is running high temperature baseboard and radiant, and this is the only way to keep the temps low for the radiant.
Rick

CBRob

Just dhw and a hx applied snow melt loop. No radiator or other high temp circuit

I'll learn more about it then come back with questions
Thanks.

HomerJSmith

A Munchkin is a condensing boiler and must be piped in primary and secondary configuration.

I think that the only reason to pipe an injection loop is because the injection loop is at a different temp than the supply water temp. For instance, baseboard and radiant floor.

The Munchkin must be cleaned between 3 and 4 yrs if it has high usage (SH and or Indirect DHWS).

CBRob

> @rick in Alaska said:
> I am not up on the Munchkin, but if it is condensing, you should be able to pipe it direct without the injection loop. However, it might be piped so that it is running high temperature baseboard and radiant, and this is the only way to keep the temps low for the radiant.
> Rick

Rick, the snow melt system is the only other heat demand besides dhw.
It uses a hx, I bet it would be fine using temps about the same as the infloor heat.

HomerJSmith

Au contraire, mi Capitan! Snow and ice melt takes a lot of BTU's. The way you get BTU's to the S&I melt sys, is to increase the flow or increase the Temperature. The flow is limited and the Temp is not, so you increase the temp.

I don't fully understand your sys. How do you heat your house if the Munchkin is just doing the indirect tank and the S&I melt?

The flat plate heat exchanger between the boiler and the S&I melt is there to run anti-freeze in the S&I melt part?

Why is there an injection sys need, at all? Where did this "infloor heat" come from?

CBRob

I meant the only other heat call besides the infloor heat is the snow melt.
It's a small area too, just a couple hundred sq ft if snow melt.

Just trying to determine why the injection pump is used instead a typical primary and secondary loop.

CBRob

The system has a primary loop, with the dhw, injection pump loop and snow melt tee ed into it.

I'm not sure yet how the.controls prioritise ch and snow melt.

Snow melt is on a basic manual tekmar 650 control.

Zman

The better way to do this would be to eliminate the injection loop and run the boiler on outdoor reset with DHW priority. You would likely need to revisit the sizing of the snowmelt HX so that it can provide adequate energy to the snowmelt using the lower boiler water temps.

CBRob

The munchkin boiler is all up and running now.
It was a problem with the tekmar injection control.
It was a simple replacement and a good easy troubleshooting project for me.

I have the injection temps set a little high for now just to speed up the process of getting the house up to 65.
With the outdoor setback and correct setting it was only sending 85 degree water into the infloor heat. I raised it to about 100 degrees.

This munchkin does not have the add on kit called vision.
It does not have a outdoor temp input.
It only has one temp set point for everything and the primary loop pump runs 24/7.

I think it is 18 years old, not sure if it's worth the 700.00 kit that would let you set a different temp for dhw and ch
I'm glad I spent some time there, it allowed me to notice the uncapped .5 inch hole in the flue pipe.

HomerJSmith

Is your Munckin a Revision 1? The Vision 1 kit consists of an outdoor sensor and a DHW tank sensor for an indirect tank well.

You can try Jupiterheating.com for a Vision 1 kit. If you need to redo the control it can be about 1/2 of your estimate for the whole thing.

You can program the outdoor reset in to your Munchkin yourself, there are four values that can be changed once you enter programing.

The label on the boiler will tell you the Revision #.