Oil boiler water temp too hot

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Old 11-07-12, 01:39 PM
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Oil boiler water temp too hot

I have a Newmac oil fired boiler that I just fired up for this season. The burner comes on, the pump for the appropriate zone starts (it's a 2 zone system) and begins to heat the house. However, after about 10 minutes the burner shut off. After restart I watched the temp gauge and it slowly climbs to approx 200 degrees and then the burner shuts off. I'm guessing this means the aquastat is operating correctly, so my question is, if the water is circulating normally why would the watertemp rise so high. I had the boiler serviced last fall (one year ago) and if I'm not mistaken the tech replaced the nozzle. I had no problems with the boiler last winter so I'm assuming that the nozzle is the correct size. What else might cause the water temp to rise so high when the system is running? Any suggestions as to what I might check next would be greatly appreciated. Thanks.
 
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Old 11-07-12, 07:08 PM
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First I have to ask the question of where is the high limit set? If it is set at 200 that would be why it is shutting off at 200f.
The boiler will cycle on and off if just one zone is calling due to the fact that if the boiler is properly sized and only one zone is calling the boiler is about 100% over sized due to half the load is being heated.
 
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Old 11-08-12, 01:50 AM
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Thanks for the quick reply. It seems that in the past I don't recall the burner cycling on and off every 5 minutes or so, once the water gets hot. Possibly it did and I just never noticed it before. This seems like a pretty inefficient way to heat a home. I believe that when the boiler was installed around 6 years ago they said that the water temp would normally run around 170-175 degrees. I'm going to check the high setpoint on the aquastat just to make sure it's shutting off at the selected temp. I'm going to say I think you would normally want to shut the burner off before the water reaches 212 degrees, so around 200 or so seems reasonable.
 
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Old 11-08-12, 05:43 AM
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A normal setting is 180f.
 
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Old 11-08-12, 11:59 PM
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Yes, it was set for around 200 degrees. I dialed it back and now it's turning off at about 190. I'll dial it back to around 180 and then see how it goes. Thanks for giving me what would be considered a normal high temp setting since I don't find any hard figures in the manual for the boiler. I suppose different units from different manufacturers have varying specs but what is a good average water pressure reading for these systems at max (180) temp? The T&P valve occasionally releases water and if it does this more than once or twice then the low water monitor shuts the boiler off. My T&P valve is a 30 psi unit and also says 535,000 BTU. The boiler is a 118,000 BTU unit so I'm wondering if I should put in a unit that is closer in specs to my boiler, or doesn't the max BTU spec of the valve matter? Thanks again.
 
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Old 11-09-12, 01:48 PM
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Hi mscheel Ė

The T&P valve occasionally releases water and if it does this more than once or twice then the low water monitor shuts the boiler off.



Iím not an expert by any means. I've just picked up some knowledge from following this forum for quite a while plus maintaining my own system. But I bet rbeck or one of the other experts on this forum will tell you something is wrong if your relief valve is spewing out water once and a while , then forcing your LWCO to shut you down.

I think that means you are experiencing a pressure rise out of range? I donít think you should ever be seeing a water release if your system is operating properly? Doesnít seem like lowering your temp from 200 down to 180 would solve that problem either, but I certainly could be wrong about that!

I hope the pros will weigh in.

Good luck!
 
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Old 11-09-12, 10:44 PM
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The T&P valve occasionally releases water
Your problem is almost certainly at your expansion tank.

Please read this 'sticky' post:

http://www.doityourself.com/forum/bo...sion-tank.html

That valve you are referring to is only a PRESSURE valve, not a TEMPERATURE and PRESSURE as they use on domestic water heaters.

The max BTU of the valve MUST be higher than the BTU rating of the boiler. ASME codes dictate the size of the valve. No, you don't need to replace it for that reason.

It wouldn't be a bad idea to replace it as routine maintenance every 5 years or so.

what is a good average water pressure reading for these systems at max (180) temp?
Depending on the height of the building... up to 2 stories tall, the pressure in the boiler should be 12 PSI when the boiler is COLD... and when it heats up the pressure might increase as much as say 10 PSI or so. It must not go above 27 PSI ( which is 10% less than the 30 PSI rating of the relief valve)

Might as well read this one too:

http://www.doityourself.com/forum/bo...ure-gauge.html
 
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