No heat in one zone

Hi there,

My house has a hot water heating system with a gas burner and one circulation pump (TACO 007-F5). It has 3 zones controlled by 3 separate thermostats (one upstairs, 2 downstars). A week ago, one night, the zone upstairs kept heating even the temperature has reached what the upstairs thermostat was calling for. So, I did a little investigation and determined that the circulating pump was bad. I also found that the zone valve (TACO 571-2) on this zone was bad too. I went to home depot and got these 2 parts and installed them over the weekend. After filling the system up, I found that one of the zones downstairs had no heat no matter what I tried - I did not have any problem to get heat in this zone prior to the parts installation as I recall.

Here is what I have done to investigate this issue. First I want to know whether the zone valve in this zone is bad. I isolated the other 2 zone, then I shutoff the shutoff valve before the circulator, set the temperature above the current temperature to force the thermostat to call for heat in this zone. then, I opened the drain valve just like I am going to drain this zone. When water comes out off the drain valve, I can feel hot waters is getting to the pipe of this zone. So, the zone valve is working as it should. Now, it looks like the new circulator pump might be at issue. I forced the thermostats on the other 2 zones to call for heat, and heat did get to the other 2 zones. However, my wife thought the heat was much slower than before to get to the 2 zones (subjective?).

My questions:
- Could it be because the new circulation pump is bad? I mean, it is new, sealed, etc..
- Could it be the control box on the burner such that the relay stopped functioning for this zone only?
- Any other probability for the problem?

 

For the zone that isn't heating, see if you are getting 24V to the zone valve when heat is called for.

I'm uncertain how you determined that the original pump was bad? You seem to be saying that it ran when it should have been off? That would suggest a problem with controls, not the pump.

The isolation valves ahead and behind the circulator are there to allow pump maintenance without draining the system. The pump should not be be run with either the discharge valve or suction valve shut. It can cause damage to the pump.

If your new pump runs at all, and one or more zones heat, then I would say it is working OK. Is the new pump the same model as the old one? If not, the head-flow curves of the two pumps should be compared to make sure they are equivalent, hydraulically.
Doug

 

If you drained the system, You may have air in the lines that can cause the pump to quit pumping if its airlocked. You also could have air trapped in the baseboard and there should be a vent on them to release the air until you get water

 

Both are very good thoughts, David and gilmorrie. David: I will try to purge air again to see if it improves. gilmorrie: 1. For the zone that is not heating, the voltage is correct on the TACO 571-2. On the terminals 1,2,3, it is ~24v on 1-3 and 1-2, 0v on 2-3. 2. I thought the pump was bad is because it was making noise the night when the heat wouldn't stop for the zone upstairs. I figured the heating not stoping was because the zone valve in that zone was bad (it wouldn't close when the thermostate was not calling for heat). Note that this zone is now owrking okay but the heat does seem to be very slow to get. 3. I do not have a valve between the boiler and the circulation pump - so I drained the system to replace the pump. 4. The new pump is exactly the same as the old one, TACO 007-F5. Okay, here is some more information. I did notice the heat is getting to the other 2 "good" zones very slowly (one upstairs, one downstairs). It may be air in the system. I took a picture of the boiler control, and here it is: http://www.myagilent.com/Boiler_Control.jpg (link is case-sensative) Please note that the voltage from the 2 terminals that lead to the circulation pump is always 0V no matter the thermostate is calling for heat or not - is this correct? Thanks a lot!

 

I am really puzzled. I did get some air out but it did not help much. The "dead" zone is still cold.

I attached the controller picture in my last post
Can soneone tell me if this is good: the line voltage between the 2 terminals connecting to the circulator is always 0v even when any of the thermostat is calling for heat. If there is no voltage, the circulator will not run, right? But how come I still get somme heat in the other 2 zones although it is very slow (comparing with what it was before)?

Thanks!

 

In this post:

http://forum.doityourself.com/boiler...-readings.html

NJ Trooper says when no zone is calling for heat, terminals 2 and 3 on the zone valve should have 24VAC, but mine does not. When no thermostat is calling for heat, there is no voltage reading (all 0v) between any 2 of the 3 terminals of the zone valve. Does this mean the transformer on the controller (Honeywell L8124A/C) is bad? How do I do to tell for sure?

Thanks!

 

There is one definite thing here ...

You should most definitely have 120 VAC on terminals C1 and C2 when the system is calling for heat... but ONLY when the boiler is above the LOW LIMIT setting of the aquastat. Your setting on the LL is 160 and the diff is 15 ... if the boiler temp is below 165, the circulator will not run ...

I would lower the HI to 180, the LO to 140, and the diff to 20 .

You may still have air in the zones ... show us some more pictures that show the valves / drains / and pipes around the boiler ... you may not be purging the zones properly ...

 

Thanks, NJ.

When I said the line voltage between C1 and C2 is 0, I mean "0" all the time, even the boiler temperature is at 180 - above the LO (this is when the boiler shuts itself off). One thing though, the boiler does fire up from time to time when the temperature is below some level (LO?) and shuts off when temperature is at ~180. The circulator does not seem to run at any time.

This has me focus on the transformer of the controller (the brown-yellow-ish square thing on the up-right corner). I suppose the line voltage between the 2 terminals TT (I mislabeled it as "From Thermostat" - actually, they connect to terminals 2 and 3 on the zone valves.) should be 24VAC at some point (when no zone is calling for heat and the boiler is off), but I get no voltage at all, any time. Does this signal a bad controller or just a bad transformer? If it is the transformer, can I replace it? I almost want to connect another transformer to TT and test this theory - is this safe?

Thanks!

Long

 

Based on your description, it sounds as though either the transformer secondary, or the relay coil are open. It could be a bad solder connection.

What happens when you manually push down on the top of the relay arm ? Does the circ run and the burner fire ?

You can't easily connect an external transformer to that aquastat. You don't have access to the terminal you need ... and also, you would void any UL listing. If you did have an 'incident' related to your boiler, and your insurance company discovered the fact that you've 'tampered' with the controls, they would be well within their rights to deny any claims. Is it worth it ? I don't think so ...

If the problem does turn out to be a bad aquastat, buy a new one ...

 

Thanks, NJ.

If I push on the relay arm, the boiler fires up and the circulator runs - just as you expected.

In the controll box, the transformer (secondary) looks ok - just a little stuff melt as you can see in the picture. I opened the controller and the relay coil looks really bad - clear sign of burn. While I was there, I tested the 2 leads on the transformer and found no voltage (I was expecting 24VAC, right?). So, I guess the transformer is bad too.

I will have to buy a new controller and will post back with results.

Here is another question. On the aquastat, there are 2 terminals marked as "TT" - connected to the zone valves. Does it matter which terminal ("T") connects to which terminal on the zone valve? Currently, the left one (red) is connected to terminal 3 (bottom one) on the zone valve. Is this correct? The reason that I am asking this question is that if I have connected these terminals wrong, this might be the reason that the aquastat went bad.

Thanks as always.

 

With the TACO zone valves, it might not be all that difficult to wire them up in such a way as to feed voltage from the external zone valve transformer back into the aquastat.

But I do not believe that simply reversing the TT leads would cause any problem at all.

It is possible that the relay coil developed a 'shorted turn', causing it to draw more current, get hot, and in turn damage the transformer, because it would get hot also from the excess current draw...

Whatever the case, it does seem as though the aquastat is pooched.

 

I replaced the Aquastat (L8124A/C) and the problem is solved. I am trying to get one as a backup.

Thanks to everyone for your help!

 

Glad to hear all is working now!

Those aquastats really don't go 'bad' that often ... not sure you really need to keep one as a spare, but if you feel more comfortable having one, then sure, go ahead...

Good Luck!