Ouch! 160 degree hot water from indirect tank
#1
02-05-09, 07:51 PM
Ouch! 160 degree hot water from indirect tank
Quick overview of the system:
Buderus G124X boiler with ST-150 indirect hot water tank. Two zones each with their own Grundfos circulator: one on priority for DHW and one for baseboard heat. Circulators are controlled by a Taco relay and DHW temperature is set on a Honeywell 4600A aquastat.
The pressure relief valve tripped on the DHW tank twice last week and left me with a flood in the basement. Heater guy came out to replace valve, but the water in the tank was much hotter than it should have been. It was set at 120 and coming out 160-180 in the kitchen sink. I have a feeling the problem has been happening for a while and the pressure valve got weak over time and blew.
Anyway, the heater guy couldn't definitively say what was wrong. When the house was heating it seemed like the Grundfos circulator for the tank was allowing hot water through its check valve causing the tank to overheat. That was just a guess on my part based on how hot the pipe was when the house was heating.
This is what I observed: when the house heat is interrupted by a DHW call for heat, after the DHW is finished the pipe going to the hot water tank remains very hot until after the house heat goes off. So it's like the check valve is sticking sometimes.
But after watching the system for a few days, I'm beginning to think the aquastat might be at fault. I have it set low, 110-115, and it's still calling for heat when the water coming out is 140ish (measured with an oven thermometer).
Is there an easy way to check the aquastat? It has a copper bulb inserted into a drywell on the tank-- it's snug in there but not tight. Ambient temp in basement is about 55degF.
The new pressure relief valve hasn't blown since it was installed but the water is way too hot. What's a good plan of attack? Heater guy left me with a $200 bill for the new valve and no firm diagnosis.
Should I look at the aquastat or the circulator? Circulator is all of a 15 minute swap-out (flange valves) but it costs $100. I'm not sure if the check valves fail often. I have no idea what to check on the aquastat for an accurate temp reading.
Any advice would be appreciated. This is a great forum! Thanks!
Buderus G124X boiler with ST-150 indirect hot water tank. Two zones each with their own Grundfos circulator: one on priority for DHW and one for baseboard heat. Circulators are controlled by a Taco relay and DHW temperature is set on a Honeywell 4600A aquastat.
The pressure relief valve tripped on the DHW tank twice last week and left me with a flood in the basement. Heater guy came out to replace valve, but the water in the tank was much hotter than it should have been. It was set at 120 and coming out 160-180 in the kitchen sink. I have a feeling the problem has been happening for a while and the pressure valve got weak over time and blew.
Anyway, the heater guy couldn't definitively say what was wrong. When the house was heating it seemed like the Grundfos circulator for the tank was allowing hot water through its check valve causing the tank to overheat. That was just a guess on my part based on how hot the pipe was when the house was heating.
This is what I observed: when the house heat is interrupted by a DHW call for heat, after the DHW is finished the pipe going to the hot water tank remains very hot until after the house heat goes off. So it's like the check valve is sticking sometimes.
But after watching the system for a few days, I'm beginning to think the aquastat might be at fault. I have it set low, 110-115, and it's still calling for heat when the water coming out is 140ish (measured with an oven thermometer).
Is there an easy way to check the aquastat? It has a copper bulb inserted into a drywell on the tank-- it's snug in there but not tight. Ambient temp in basement is about 55degF.
The new pressure relief valve hasn't blown since it was installed but the water is way too hot. What's a good plan of attack? Heater guy left me with a $200 bill for the new valve and no firm diagnosis.
Should I look at the aquastat or the circulator? Circulator is all of a 15 minute swap-out (flange valves) but it costs $100. I'm not sure if the check valves fail often. I have no idea what to check on the aquastat for an accurate temp reading.
Any advice would be appreciated. This is a great forum! Thanks!
#2
02-05-09, 08:17 PM
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Domestic too hot
I suspect the relief valve opened due to pressure rather than temperature but obviously that's just a suspicion. There should be an expansion tank made for water heaters installed on the domestic tank.
From what you are saying, it sounds like the aquastat & circulator check valve could be bad.
You can check the aquastat by checking the water temp to verify it is well above the setting then kill the power, remove at least one wire from the aquastat & checking for continuity across the aquastat's terminals. If continuity is present, the aquastat is indeed calling for heat.
Since you have valved flanges for the circulator, it's easy enough to pull the circ & look for debris in the check valve.
From what you are saying, it sounds like the aquastat & circulator check valve could be bad.
You can check the aquastat by checking the water temp to verify it is well above the setting then kill the power, remove at least one wire from the aquastat & checking for continuity across the aquastat's terminals. If continuity is present, the aquastat is indeed calling for heat.
Since you have valved flanges for the circulator, it's easy enough to pull the circ & look for debris in the check valve.
#3
02-05-09, 09:25 PM
Both bad? Just my luck!
Do you think the aquastat and the circulator could have both failed? I thought they were supposed to be very reliable to begin with. The system is only 4 years old. I hope it's not falling apart that quickly! :-|
I will check continuity on the aquastat in the morning. There is an expansion tank on the DHW tank, but it's on the cold water discharge side. Is that right?
I will check continuity on the aquastat in the morning. There is an expansion tank on the DHW tank, but it's on the cold water discharge side. Is that right?
#4
02-06-09, 06:06 PM
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Expansion tank
If there is one & it is installed on the cold inlet side that is correct. It would be a good idea to check it for a bad bladder. Checking for a bad bladder in the tank is easy. Turn off the cold water inlet valve which should be upstream of the tank. Turn on a hot water spigot to relieve the pressure. Use a tire pressure gauge on the schrader of the tank. The pressure should be aprox. equal to that of the incoming water pressure.
It would be unusual for an aquastat to fail that soon but not unheard of. Having something (usually a piece of rust) to hang up in a circulator check valve is fairly common if the system has any steel pipe or cast iron radiation. The unusual thing is that it took 4 years to happen. It is most likely to occur shortly after installation or if the system had been disturbed by draining for any reason.
It would be unusual for an aquastat to fail that soon but not unheard of. Having something (usually a piece of rust) to hang up in a circulator check valve is fairly common if the system has any steel pipe or cast iron radiation. The unusual thing is that it took 4 years to happen. It is most likely to occur shortly after installation or if the system had been disturbed by draining for any reason.
#5
02-07-09, 01:20 PM
Aquastat seems OK
I tested the aquastat using three glasses of water at different temperatures(60, 100, 140deg) and it's dead-on. It went on/off exactly as expected and took at most 10 seconds to respond. Should it have any heat exchanging lubricant where it goes into the dry-well? It's snug but maybe some cold air is getting in from the basement?
We do have black iron pipe that ties into the copper baseboard. I don't think it was disturbed recently, but we did have our boiler cleaned about 2 months ago. He didn't do anything with the pipes or drain anything, he just cleaned the boiler and the flue.
Not to go off on a tangent, but... when someone asks for their heater to be serviced, is it too much to think the tech will know what needs to be done?
I just happened to glance in the Buderus service manuals and the system should have been purged (I don't think it has been in 3-4 years), hot water tank drained and visually inspected, anode checked for size, etc. I told him this is the first service since it was installed almost 4 years ago. Tell me what it will cost to do a full service and let me make the decision on what I will get done. !!!!
I'm losing faith in the service industry to do the job right without a lot of hand-holding. Even the guy who fixed the pressure relief valve took some prodding before he acknowledged that a bad valve wouldn't cause the water to be 160deg. Should I have to know this???
Sorry, had to vent. I have a replacement circ which I'm going to install. Would it hurt to put a brass screen filter before the inlet, something like what's used on a faucet? Or am I asking for more problems.
And I'll remove the check valve on the old one and see what that looks like. Hopefully that's it!
We do have black iron pipe that ties into the copper baseboard. I don't think it was disturbed recently, but we did have our boiler cleaned about 2 months ago. He didn't do anything with the pipes or drain anything, he just cleaned the boiler and the flue.
Not to go off on a tangent, but... when someone asks for their heater to be serviced, is it too much to think the tech will know what needs to be done?
I just happened to glance in the Buderus service manuals and the system should have been purged (I don't think it has been in 3-4 years), hot water tank drained and visually inspected, anode checked for size, etc. I told him this is the first service since it was installed almost 4 years ago. Tell me what it will cost to do a full service and let me make the decision on what I will get done. !!!!
I'm losing faith in the service industry to do the job right without a lot of hand-holding. Even the guy who fixed the pressure relief valve took some prodding before he acknowledged that a bad valve wouldn't cause the water to be 160deg. Should I have to know this???
Sorry, had to vent. I have a replacement circ which I'm going to install. Would it hurt to put a brass screen filter before the inlet, something like what's used on a faucet? Or am I asking for more problems.
And I'll remove the check valve on the old one and see what that looks like. Hopefully that's it!
#6
02-07-09, 02:25 PM
Jim, I'm in total agreement with the level of 'service' that ppl get nowadays... it totally 5uck5... (unless of course you can talk Grady into a road trip! 
)
My belief is that there is no reason at all to purge a system unless there is a reason to do so. i.e. system opened for service... once the air is out, it's out, leave it out and leave all that nasty old oxygen starved water in.
"Hot water tank drained..." do they mean the expansion tank? or are they talking about an indirect water heater tank? The mention of an anode rod makes me believe that they may be... it's a good idea for the homeowner to flush sediment and debris out of ANY hot water heater periodically... like every few months or so... or as water conditions dictate.
You would not want to install a 'screen'... but if you feel the need to strain the water, a WYE STRAINER _could_ be used ahead of the circ... you would have to do a little re-piping to make room for it though. Probably not a necessity... check out the pump and see what's what, then decide.
If it's 'snug', it's probably OK, but thermal compound wouldn't hurt I guess... I doubt if the ambient air would have any affect on it.
)My belief is that there is no reason at all to purge a system unless there is a reason to do so. i.e. system opened for service... once the air is out, it's out, leave it out and leave all that nasty old oxygen starved water in.
"Hot water tank drained..." do they mean the expansion tank? or are they talking about an indirect water heater tank? The mention of an anode rod makes me believe that they may be... it's a good idea for the homeowner to flush sediment and debris out of ANY hot water heater periodically... like every few months or so... or as water conditions dictate.
You would not want to install a 'screen'... but if you feel the need to strain the water, a WYE STRAINER _could_ be used ahead of the circ... you would have to do a little re-piping to make room for it though. Probably not a necessity... check out the pump and see what's what, then decide.
Should it have any heat exchanging lubricant where it goes into the dry-well? It's snug but maybe some cold air is getting in from the basement?
#7
02-07-09, 04:23 PM
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Service
I agree with Trooper on the purging. One of the worst things you can do to a hot water heating system is to introduce fresh water. If there is an effective air removal system in place the system should never need purging.
As for the indirect, that is something generally not done unless the customer specifically asks.
I don't think I would install any type of screen in the line at least not without gauges on each side so you could measure restriction thru said screen.
It certainly wouldn't hurt to insulate the outside of the aquastat well but I don't think basement air is the source of your trouble but scale or other build up on the water side of the well could certainly cause the aquastat to react slowly.
As for the indirect, that is something generally not done unless the customer specifically asks.
I don't think I would install any type of screen in the line at least not without gauges on each side so you could measure restriction thru said screen.
It certainly wouldn't hurt to insulate the outside of the aquastat well but I don't think basement air is the source of your trouble but scale or other build up on the water side of the well could certainly cause the aquastat to react slowly.
#8
02-09-09, 04:42 PM
New circulator, going to clean DHW tank next...
Thanks guys for your help!
I replaced the circulator pump this weekend. Cost $70 and about 15 minutes of my time, but it doesn't seem to have fixed the problem.
Next step is to check sediment and clean the inside of the DHW tank. I may wait until Spring to do that and just keep the DHW temperature set very low (set to 105 degrees means I get 130ish water).
After checking the aquastat and now replacing the circ, I'm not sure what's left besides the tank itself. It's a Buderus 50-gal indirect and I hoped it would be trouble free for many years. I'm beginning to think the gas-fired would have been a better choice albeit not quite as efficient. At the very least they are more easily understood when someone comes out to service the system.
Quick question re: purging. We have a Supervent on the system which I believe removes air in the system. I shouldn't need to purge after replacing the circ, correct? Would I ever need to purge the system if it has a Supervent?
I replaced the circulator pump this weekend. Cost $70 and about 15 minutes of my time, but it doesn't seem to have fixed the problem.
Next step is to check sediment and clean the inside of the DHW tank. I may wait until Spring to do that and just keep the DHW temperature set very low (set to 105 degrees means I get 130ish water).
After checking the aquastat and now replacing the circ, I'm not sure what's left besides the tank itself. It's a Buderus 50-gal indirect and I hoped it would be trouble free for many years. I'm beginning to think the gas-fired would have been a better choice albeit not quite as efficient. At the very least they are more easily understood when someone comes out to service the system.
Quick question re: purging. We have a Supervent on the system which I believe removes air in the system. I shouldn't need to purge after replacing the circ, correct? Would I ever need to purge the system if it has a Supervent?
#9
02-09-09, 07:07 PM
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Purging
Any half decent air removal system should not need purging after the simple replacement of a circulator. Personally, I hate purge valves. Sometimes they are a necessary evil but very rarely.
I didn't mean for you to go out & spend $70 for a new circulator on my speculation.
If you would take some pictures of the boiler, tank, & nearby piping, post them on photobuket.com or similar site, & provide a link here, maybe something would jump out at us as the cause of the domestic overheating.
I didn't mean for you to go out & spend $70 for a new circulator on my speculation.
If you would take some pictures of the boiler, tank, & nearby piping, post them on photobuket.com or similar site, & provide a link here, maybe something would jump out at us as the cause of the domestic overheating.
#10
02-11-09, 09:16 PM
Pictures!
Sorry Grady, I didn't mean to imply that I bought the circulator on your suggestion. I bought it right after the heater guy told me it was probably bad, but the store is far and doesn't have weekend hours so it wasn't easy to return. I figured I'd give it a try since I had the part. And having a spare on hand now will prevent one from ever going bad! :-)
Here are some pictures I took tonight. Sorry if they are too large... I never know how big these things are going to turn out.
Heater Room
http://i237.photobucket.com/albums/f...r_w_Labels.jpg
Back of Boiler
http://i237.photobucket.com/albums/f...r_w_Labels.jpg
DHW Tank
http://i237.photobucket.com/albums/f...W_w_Labels.jpg
Taco Control
http://i237.photobucket.com/albums/f...MG_0164_30.jpg
Top of Boiler
http://i237.photobucket.com/albums/f...MG_0156_30.jpg
The room is a mess, but does it look like a decent setup?
Once this is figured out, my next step is to get the radiant pressure tested. It's copper in concrete and the original installer "guaranteed" it would leak and recommended against hooking it up. Before we look for alternative means of heating the basement, I think I should double check it.
Here are some pictures I took tonight. Sorry if they are too large... I never know how big these things are going to turn out.
Heater Room
http://i237.photobucket.com/albums/f...r_w_Labels.jpg
Back of Boiler
http://i237.photobucket.com/albums/f...r_w_Labels.jpg
DHW Tank
http://i237.photobucket.com/albums/f...W_w_Labels.jpg
Taco Control
http://i237.photobucket.com/albums/f...MG_0164_30.jpg
Top of Boiler
http://i237.photobucket.com/albums/f...MG_0156_30.jpg
The room is a mess, but does it look like a decent setup?
Once this is figured out, my next step is to get the radiant pressure tested. It's copper in concrete and the original installer "guaranteed" it would leak and recommended against hooking it up. Before we look for alternative means of heating the basement, I think I should double check it.
