Buderus Hot water Boiler & Taco SR502 Switching Relay Trouble

Grazi57

Hello Everyone...Happy Holidays (whatever it is you may practice)

Let me start by making this very clear - I have no idea what I am doing.

What I do know is my Bederus Hot water furnace is not getting hot water to certain places at my home to heat it. I have a two zone house, but nobody can fully identify where the zones begin and end not to mention that I also have forced air heat besides just the water. But back to the point...

I called a technician to visit my home today as one of the rooms in my house was 20-30 degrees below the rest of the houses temp in the early morning. I also was having trouble with there being no heat coming with other rooms in the house but this was before I learned how to "bleed" out the air from each of these units.

In any case the gentleman said that he believes that I had a blown fuse in my Taco SR502 Switching Relay unit. He said it would cos around $200 to repair. He told me that the very special fuse was hard to get and they had to order it...Because he couldn't find any of the replacement ones.

I'm not an idiot, and after he left I quickly found that the fuse cost $22 on Amazon. However he failed to mention that there were two brand new fuses attached to the unit itself. So I found what appeared to be the blown fuse (It was cloudy and black, where as the other two looked clear and brand new). So after turning off the power I replaced it, turned the power back on and POW! The fuse was fried again...

Now I have a feeling that maybe this guy wants me to get a brand new unit, which is running around $150 from what I can read... But I wanted to see if any if you could help me. I'm assuming that maybe too much juice is going through that one fuse area? But as I mentioned, I know very little to this regard... Just trying to safe a few $'s Thanks for the help!

- Mike in Eastern PA

Grazi57

HVACNUT

First, this forum doesn't discuss pricing so leave numbers out.
Zone 2 is having the issue? What does zone 2 heat? Rads, hydrocoil, radiant?
And what type of thermostat controls that zone?
That fuse protects the 24v circuit for that zone.
If you remove the zone 2 thermostat wires from R and W at the top of the panel (don't let the wires touch metal or each other as there might be a short somewhere), then jump R and W (with a new fuse). If the circ runs and the fuse doesnt blow, then the problem is somewhere back down the line. At which point you need a qualified pro knowledgeable in control wiring. If the fuse blows, the problem is the Taco board and needs to be replaced.

Grazi57

Sorry about that, as for which zone is having problems - Yes it is Zone 2. It is a Radiator water heater.

Its an electric thermostat, or are you referring to something else?

unclejohn

Turn off the power like you did too replace the fuse and disconnect the white and black wires to zone two on the bottom of the control and replace the fuse again and see what happens. if it dosen't blow you have a bad pump or wiring issue to the pump. If it blows again with the wires disconnected probably the control.

Leon82

There should be a backup fuse in the cover

HVACNUT

@Grazi57, I edited my first post. Try a few things

Paul48

Shut the power off to the sr502. Carefully mark and disconnect the black and white wires from the 2 zones. Replace the fuse and turn the power on. If the fuse blows, you can assume the 502 is shot. If it doesn't there is a problem with the circ or the wiring to it.

Grazi57

So at this point, no matter what I have to use a fuse to find out where the problem is?

Well at the moment I only have one fuse left. Where could I drive to get a fuse on a Sunday? Home Depot?

This is the fuse BTW: https://www.amazon.com/Taco-Inc-SR5A005RP-AMP-FUSE/dp/B00QW27KW6/ref=sr_1_fkmr1_1?s=industrial&ie=UTF8&qid=1513465676&sr=1-1-fkmr1&keywords=taco+sr502+fuse

HVACNUT

No to Home Depot. An HVAC supply or Taco distributor is the best bet.

Grazi57

Ok Thank you!

So at this point we are just trying to pinpoint whether it is the 502 unit itself or the wiring... Ugh what a mess.

I'm going to hunt around the local area to find the best price/Certified guys. Thank you guys!

HVACNUT

You have another fuse. Live on the edge!
He that leaveth nothing to chance will do few things ill, but he will do very few things.

Leon82

The home Depots near me usually have a 503 on the shelf if you end up needing a new one and need to replace it sunday

Jamie Hall

HVACNUT said:

You have another fuse. Live on the edge!

He that leaveth nothing to chance will do few things ill, but he will do very few things.

or... "Behold the turtle. He progresseth not unless he sticketh out his neck."

EBEBRATT-Ed

If there is a any Radio Shacks left in your area they will probably have a fuse

ChasMan

Lets pile on glass fuses .. where can we get them on Sundays.. Well, Radio Shack.. & Home Depot. I think it is a GMA5 in those taco boxes.

Alan Welch

Looks like both thermostat wires for zone 2 under same terminal?

HVACNUT

> @Alan Welch said:
> Looks like both thermostat wires for zone 2 under same terminal?

Eagle eye! Good catch. It wouldn't cause the fuse to blow, but it will leave him without heat.

hot_rod

Fuses really are not the best troubleshooting tool For what you invest in fuses you could buy and inexpensive VOM. A meter to help track down the short.

Paul48

I show 43 in stock at my Home Depot.

BobC

Amazon is ripping you off, iot's probably a pricing error, try these folks -

https://www.supplyhouse.com/Taco-SR5A-005RP-Replacement-Fuse-5-Amp-10-Pack

If it were me I'd start to check out everything with a multimeter, when a fuse blows like that you have a dead short somewhere. It might well be a pinched wire - examine any wires that have been stapled to see if they got to energetic with the staples.

Bob

Paul48

I don't have an electronics background, so if it blew with the circs disconnected, I'd be replacing the SR anyway.

BobC

The fuse is there to protect the SR, just because the fuse has blown does not mean the SR is failed.

Figure out exactly what is connected to the output side of the fuse and disconnect all of them. Start by disconnecting the wire that that fuse feeds and then power it back up with a new fuse, if the fuse does not blow the SR is probably fine.

Next reconnect that wire but disconnect anything it feeds so only the wire will remain connected to the controller.Power it up, if the fuse blows you have a short in the wiring. If the fuse does not blow reconnect each item it feeds in succession and see if the fuse blows when an item is reconnected.

If the fuse blows when something is reconnected you have found the problem

EDIT:

On closer examination of the picture I see that fuse is on the AC input of the SR. In that case I would disconnect both output channels and then see if the fuse blows. If the fuse blows with both output channels disconnected the SR is probably bad.

If the fuse does not blow, reconnect one channel at a time and power it back up. If the fuse blows after connecting one of the outputs, the problem is probably in something connected to that output. In that case follow the procedure above to isolate the defective part or wiring.

Bob