CGa Series 3 Gas-Fired Water Boiler - 4 wire zone valves

SENWiEco

Good evening all,

I am assisting a neighbour install a new Weil Mclain gas boiler. Today we fired it up, and after running for 15 mins or so, the boiler lost power. After going through manual troubleshooting, it was determined the onboard boiler supplied transformer had blown (secondary circuit is 24VAC 40 VA).

I have tried to research why, including a lot of searches on this site, and I am still not sure why. Any assistance would be greatly appreciated.

Details: 6 zoned system utilizing honeywell 4-wire zone valves. All the zone valve motors are powered by a secondary 'customer supplied' transformer mounted outside of boiler. All of the zone valve end switches were wired in parallel with applicable t-stats (Believe - it is typical rat nest - but has been working fine for decades on old boiler) into the T-T on the boiler t-stat pigtail. No 'smart' thermostats anywhere.

boiler wiring diagram.

The manual mentions "DO NOT connect directly from 3-wire zone valves to the T-T terminals on the boiler. When using 3-wire zone valves, install an isolation relay. Connect the zone valve end switch wires to the isolation relay coil. Connect the isolation relay contact across the boiler T-T terminals"

As these were 4-wire valve actuators, we ignored this.

1) does the 3-wire warning also apply to 4-wire valves with limit switches?
2) is this because the 40VA does not have capacity to supply boiler AND an extended limit switch circuit?
3) Do I need an isolation relay (I have a Honeywell R8285D 1000 transformer/relay assembly off old boiler, but unfortunately, I was not around when old boiler was removed)
4) Does this relay go on the boiler transformer, or the acc zone valve motor transformer.
5) in either case, how is it wired up?

It looks like the original blown relay was provided 120VAC through the black and white wires which would obviously go to the primary side of trans. Then yellow would be 24VAC and the blue would be COM?

This is as far as I have made it. If this has been dealt with before, please just point me to thread(s) and I will read through. I searched several different ways and just saw discussions about relays needed when smart stat needs 'C' wire.

Many Thanks in advance!

Big Ed_4

You have a short to common some where . You first need to 3 amp fuse the new transformer . The problem is in your wiring , redo it .

Big Ed_4

The 40va secondary transformer may too small for six zone valves . Check the amp draw of the zone valve used x 6= total amps T amp x 24V = VA needed . Alway go larger .

I am thinking the HW draws .3amps (but check) 43VA minimum . 50VA or better 70VA , I would recommend .. The 50 and higher Honeywell transformer with the built in circuit breaker is what I use..

EdTheHeaterMan

To follow up on @Big Ed_4 recommendation you can purchase a box of 3 Amp automotive fuses and connect a spade connectors to the transformer R terminal and the other end to the wire that came off the R terminal of the transfromer
This will reduce the chances of letting the factory installed smoke from leaving the transformer.

As far as the zone valve transformer is concerned, @Big Ed_4 is spot on. Honeywell recommends that no more than 4 zone valves get connected to a 40VA transformer. (40VA is the most common transformer used in HVAC control systems). With 6 zone valves you may need to use two 40 VA transformers or one larger transformer like the 70 VA.

When I had professional customers come into the supply house (during my short time as the HVAC specialist at Weinstein Supply Pleasantville NJ) I would strongly suggest that the Rat's Nest of wires can be solved with a Taco ZVC406

So to be clear which transformer failed? The transformer inside the boiler or the transformer outside the boiler?

SENWiEco

Many thanks to @Big Ed_4 and @EdTheHeaterMan.

Many thanks for fuse recommendation. Will make sure installed.

Re amperage capacity, does not the zone valve amp draw stats only refer to the motor circuit? These are already being fed with the same external 'customer supplied' transformer that was on the old boiler. This too is a 40VA but 26.5VOC instead of 24V.

It is the onboard transformer that blew (one supplying 24V power to boiler control panel). The only thing connected to this transformer is the boiler with supplied accessories and the zone valve limit switches.

@Big Ed_4 you mentioned a short - this has got me thinking.

After finishing the piping and wiring installations yesterday, I went back today to do start up. Everything was working fine (once I remembered to open the return ball valve :-( ). I had cleaned up and was about to start taking all of my tools home when I heard dripping. Turns out owner had a bleed screw open on one of the rads upstairs. He claims, and I believe, this vent had not been touched for a decade. I believe it had become plugged with debris during previous work (so they thought it was closed), and the flushing done during the installation, and then the hot water circulating through during initial startup, dislodged the debris, with the resulting mess.

At the time the boiler was firing. I yelled out for owner to turn off system while I rushed to shut off all circuit ball valves. It was after we cleaned up and refired the boiler, that the transformer blew. The dwelling does have a past history of rodents, with a lot of AC wiring in the general area of the leak, needing to be replaced or repaired due to gnawing about 12 years ago.

I am now wondering if there is a thermostat wire that is damaged and now shorting out because surrounded with wet insulation??

I did not put the two events together, I just assumed I had done something wrong and the trans was overheating and blew after a period of time. If the end switches do not have a particula VA need, then Ed's first call that I have a short, may be the right one.

HVACNUT

You mention 6 zones buy only 4 zone valves. Explain. 

If only the end switch wires are going to the thermostat connection on the boiler and the boiler fuse blew, then the end switches aren't wired correctly, or there's a factory wiring issue. 

Try disconnecting the end switch wires from the thermostat connection at the boiler, then jump the thermostat connection at the boiler and see if all is good. Manually open the zone valves first or it will hit high limit very quickly. 

SENWiEco

@HVACNUT - don't see where i mention 4 valves, there are 6 valves. Going back and testing your recommendation now.

SENWiEco

Many thanks to @Big Ed_4, @EdTheHeaterMan & @HVACNUT. I jumper-ed TT (removing the end switch loop), put back the original 'blown' transformer, and unit is now firing. Tested secondary on trans and it it putting out 28.5V which I assume is close enough to 24V. Looks like the manuals trouble shoot section is a bit off to suggest trans was blown.

I will now start from scratch on the rats nest, terminating everything to terminal strips instead of a maze of marrettes.

Can you suggest how I go about finding the circuit that may be shorted out??

EdTheHeaterMan

Since the transformer that you determined was "blown" based on the trouble shooting, And by connecting the "blown" transformer made the boiler operate properly, You do not have a "blown" transformer. So what condition did you observe that made you believe it was a blown transformer?

EdTheHeaterMan

Although this will be an added expense, this will be a great help in diagnosing zone thermostat, zone valve and zone wiring faults.
There is a green power lamp to let you know that there is power to the control. Each thermostat has a lamp that will indicate the thermostat is calling for heat. Finally each end switch has a lamp the let you know the valve opened and the end switch closed.
The rat's nest shown here has no such diagnostic lamps
Even though the valves and thermostats have worked for years you are having a problem now that is most likely in that nest. One of those wires has made something open when it should be closed. Or, it could be a bad end switch on a valve, or a loose connection or a rodent damaged wire. Make it easy on yourself and charge your customer for the new recommended equipment.

If this is a DIY. Then this is an easy project connecting one wire at a time. Just match zone thermostat to zone valve on each zone. do one zone and test it, After that checks out, then all the wires go to the same places on all 5 other zones

EdTheHeaterMan

But you want to know how to fix it now! Right?

Whenever I came across this type of mess on a zone valve job that was giving me issues, I would remove all the connections, wire nuts and wires from screw terminals so I could start from scratch. This is time consuming, but will eventually find the source of the problem.

Step 1. Turn off power for the transformer to the zone valves and power off to the boiler. Disconnect all the zone valve wires thermostat wires and transformer wires,

Step 2. Wire zone one thermostat R to the transformer R. Then wire the thermostat to W to the zone valve motor. Then wire the other zone. valve motor wire to the C on the transformer. Turn on power and test to see of the valve opens on a call for heat and closes when the call fro heat is satisfied.

Step 3. Turn off power and connect the end switch from zone 1 to the T T or thermostat terminals to the boiler. Turn the power on and test the zone by calling for heat and see if the boiler starts after the valve opens.


Step 4. If that is successful then repeat step 2 and 3 on each zone valve one at a time.And if I have not fried the transformer yet, this is about the time I remember to put on a fuse so I don't burn out any transformers

Step 5. Test each zone individually after completing that zone
Step 6. Test all zones at once to see if there are any issues when all the zones are calling
Important: every zone valve must be wired identical, so I recommend that Transformer R goes to Thermostat R. Thermostat W goes to #1 on taco zone valves or TH on Honeywell zone valves. TR on honeywell zone valves goes to C on the transformer. This is important so you done let the factory installed smoke out of the transformers.

SENWiEco

@EdTheHeaterMan - Many thanks for all your assistance and information.

To answer "what condition did you observe that made you believe it was a blown transformer", I was using the manual diagnostic chart.


Was down to bottom right test and answer was no. At least was yesterday. Did not test today. As soon as I plugged in the end switch circuit, the entire boiler would go dead (no lights).

But after the feedback here yesterday, and the assumption I had actually done it right, and it was an outside issue, I tested the transformer which I brought home. Was OK.
SO then I tested per @HVACNUT and just jumpered T-T. All ran fine. At this point I knew it was the rat nest, and I have just finished the redo and am FREE AT LAST.

This is for my senior neighbours. He is a self-proclaimed 'cheap Scot'. He is also old school and does not like computerized stuff.

And I am not a tradesman, just a fairly well informed owner-builder. His son was a plumber, but was only available Sunday's and not comfortable with wiring and controls.

SO I have been there since Thursday installing the new boiler, acc, and now rewiring all zone valves. I did find one t-stat circuit that returned odd and oscillating voltage. Fortunately, was easy to change out through crawl space. (used a power puck transformer to test t-Stat circuits with T-Stat removed). Odd thing was that the old cable looked fine when removed, but I guess could have been cracked conductor in the sheathing (over 50 years old and had a very sharp bend).

All is now complete, operational, and most importantly, all zones and wires have been marked. Still have to zip-strap stuff up, but here is before and completed. I do have 3A fuses on both the valve motor and the valve end switch circuits. (I was NOT responsible for the valve 'tree'. This was existing work)

Thanks everyone for the help getting me through this!

HVACNUT

Is the burner compartment facing the back wall?

dko

That bosch tankless is a powervent. though the old manual says you can use 26ga galvanized flue, it must be gas tight and sealed with high temp sealant.

The vent shouldn't be combined with the boiler nor vented into the chimney.

hot_rod

Read through the venting section of the manual

If that is a power vent heater, as @dko suggested the venting you have may be wrong , possibly dangerous

EdTheHeaterMan

Based on the pictures you posted, I have updated my drawing. But there are still no diagnostic lights like the control offers
I know, I know. this is no help... I'm just being a smart donkey

EdTheHeaterMan

HVACNUT said:

Is the burner compartment facing the back wall?

It appears that it is facing the back wall. However this picture before the boiler was installed shows access.

Not the easiest situation for service but not impossible. I might have considered a redesign of some type.

SENWiEco

EdTheHeaterMan said:

HVACNUT said:

Is the burner compartment facing the back wall?

It appears that it is facing the back wall. However this picture before the boiler was installed shows access.

Not the easiest situation for service but not impossible. I might have considered a redesign of some type.

As pointed out, there is good access to the front of the boiler via a removable panel in living room. Access to all components isn't really that bad for such a small closet. The dirt separator and boiler drain are accessible on the left, all zone valves are easily reached. As us circulator. For the expansion tank, removing the exhaust venting allows easy access to spin off and on.

Would I have done differently if my house - yes. First of all getting rid of the zone trees and installing proper headers with zone actuators (like caleffi - I have these on my system). This would free up a LOT of space to redesign layout.

SENWiEco

dko said:

That bosch tankless is a powervent. though the old manual says you can use 26ga galvanized flue, it must be gas tight and sealed with high temp sealant.

The vent shouldn't be combined with the boiler nor vented into the chimney.

I will check, but I do not believe this is power vent. This is probably 15 years old or so. Definitely does not sound like a power vent. The exhaust duct seams will be sealed once the boiler has run a few days to make sure no problems have crept up. This is an inside chimney, quite large and has great draft. There is also CO monitors installed on both floors. Also lots of make-up air.

But I will make sure this is not a power vent.

dko

Sorry, thought they only made it in power vent- but I see they did have another version.

Manuals for both models attached

SENWiEco

dko said:

Sorry, thought they only made it in power vent- but I see they did have another version.

Manuals for both models attached

No problem - is important enough to dbl-check. They have a GWH-425-HN-N, so no power venting.

EdTheHeaterMan

Now that the venting issues are resolved, (except for the fact that the sections of single wall pipe are in the wrong direction, and when installed as a connector for a Type I vent appliance there should be no type of duct tape used for sealing the joints, even the aluminum tape. So don't use duct tape for sealing those pipe joints. Just make sure they are fastened together with screws and supported properly.)
I am curious as to the zone valve wiring issue. Any resolution on your original query?

ScottSecor

Not that it makes much difference, but I have a worked on few Bosch units that appear to be identical to your unit. They are not power vented, nor is there any electricity to the unit. They are "self powered", when water flows the flame ignites. The one I'm most familiar with is approximately twenty years old.

However, I do agree someone appears to have installed the smoke pipe upside down on your unit.

SENWiEco

I am going to redo the ducting for them, I have some left over from my build. You are absolutely right - re the tape. I had not put on my ducting cap yet, when I made that comment. And the only ducting I had in my build was ventilation. I will; run a bead of high temp sealant when I put the new stuff together. There also needs to be a 1ft straight riser on the bosch before an elbow.

Re the original query: troubleshoot in the manual should have one more step, before declaring transformer is dead, and that it to disconnect zone valve switch circuit and jumper T-T (as @HVACNUT suggested).

I may never be able to tell where the problem was in the limit switch/t-stat circuit. As mentioned we replace one of the T-Stat wires, as it was not returning the 5V I was feeding it, and the values on my meter were cycling all over the place. When I looked at old wire, there was no apparent damage. I still need to do a continuity check on it, if they have not already chucked it. It could have also been a loose connection somewhere in the rat nest. Don't think it was an end switch as system is working fine now.

Even if it was the T-Stat wire and not the rat nest, the new setup will be much easier to troubleshoot and maintain. And I will probably be the person doing this. They have already told me that if I move, they will move to follow me. :-)