Boiler Pumps stops pumping after heat is satisfied


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Old 12-11-17, 10:14 AM
J
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Boiler Pumps stops pumping after heat is satisfied

Hello,
Read through these forums all morning, but could not find a specific solution to my problem.

I have a Weil Mclain CG6 Gas Boiler
Manual is here: https://www.weil-mclain.com/sites/de...6-manual_1.pdf

This is my first winter in this house in Northern NJ and the pressure valve blew 2 nights in a row ( actually had to replace it after the first incident). Through some experiments I noticed that the pump stops moving water immediately after all 3 of my zones stop calling for heat. This is causing hot water to stay in the boiler and the water temp rises causes the pressure valve to open. The heat is currently running only because all 3 zones are calling for heat on a cold day. Shouldn't the pump continue to work for a few minutes after the call for heat has ended? Is there a relay or something I need to replace?

Thanks in advance for your help.
 
  #2  
Old 12-11-17, 11:23 AM
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J,
The pump is operating properly by shutting down when the stats are satisfied. If it didn't you would get unwanted heat to the zones.

You have what they call a cold start boiler which means the boiler and pump only run on demand for heat and stop when the demand is satisfied.

Your pressure relief valve only operates on PRESSURE and NOT TEMP.

If your relief valve is going off you have other problems somewhere causing your pressure to rise.

Your R.V. is rated for 30psi and that's when it releases. Your boiler typically operates at around 15-20 psi. If it's getting to 30 you have a problem. It could be your expansion tank or your feed valve to start.

A little more info and pics of your boiler and near boiler piping would be very helpful.

Hope this helps a little.
 
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Old 12-11-17, 11:25 AM
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What is your "High Limit" set at . . . . maybe it needs to be reduced a mite so that you don't have the residual heat buildup causing the Pressure Relief Valve to pop ?

Has someone altered the settings since you bought the place . . . . or do you think the prior Owners tolerated this condition ?
 
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Old 12-11-17, 11:54 AM
J
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the high limit is set to 180 degrees.

here is a link for images
https://photos.app.goo.gl/5CJUZach57Bm3oYy1

I have not touched any of the settings. on the unit. I did replace all the baseboard heaters (with the element) for one of the zones. Also feel there is air trapped in the system, but assume those are secondary issues.

I would actually see the pump and boiler turn off at 180, then I was actually watching the temp gauge climb to around 220 before the valve opened and scared the heck out of me.

there is about 3000 sq feet ( 3 floors of heating by 3 Honeywell zone valves). The top most floor never gets hot, but I think the pump may be undersized.
 

Last edited by jaysonP; 12-11-17 at 12:24 PM.
  #5  
Old 12-11-17, 03:57 PM
S
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Pics are a little far away but the first thing I saw is that if your temp/pressure gauge if correct your boiler pressure is too low.

You are showing under 10psi at around 180 deg. which means it's very low when boiler is cold. That would be the reason why you have no heat on the 3rd floor. The water is not getting up there.

First thing would be to find out why you have low pressure. Your feed valve if operating properly and is not shut off comes factory set at 12-15psi.
You should be running about 18-20psi cold boiler pressure.

Next, although 220 is a little high your boiler can handle it and shouldn't blow the relief valve.

Your green tank hanging off the back of the boiler is your expansion tank that accepts the heated water when it expands to stabilize the pressure in the boiler. It's like the tank in your car for the heated radiator water.

What you can do is with a screwdriver or something metal tap your tank. The top half should sound solid and the bottom half should be hollow because that's where the bladder is.

If the entire tank is solid then your bladder has either ruptured or deflated and needs to be replaced.

What's happening is with the tank being water logged the heated water has no place to go and builds up pressure in the boiler until relieved by the relief valve.

I would start by pressurizing your boiler to 18psi and then starting it up and when the boiler is running tap that tank. If it sounds solid on the top and bottom shut the boiler down before the relief valve blows and change your tank.

You can push in on the Schrader valve on the tank. If water comes out the bladder has ruptured. If no water, could just be deflated and can be repressurized to the same pressure that you are going to operate your system at. It must be isolated from the system or removed to do this and to just check the charge it must be isolated or removed also or it will read system pressure which is of no use to you.

Hope this helps a little.
 
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Old 12-11-17, 04:18 PM
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Had a HVAC tech come by and he checked the expansion tank and it was OK. He took the air out of the lines and said the PSI is kind of low at 10, he bumped it up to 12, but even with heat on it does not increase in pressure. It pretty much stays the same. At this point, I am assuming the cold water pressure input value is working.

I actually getting quotes to get the unit replaced. So far I got $5500 for a Weil McLain CGA-6. My existing unit is almost 30 years old.

the tech left saying everything seems fine, but it bothers me not to know what caused the issues.
 
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Old 12-11-17, 04:47 PM
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If you feel more comfortable get in a new boiler that's fine but age really has nothing to do with it.

Unless you get a condensing boiler or a 3 pass boiler which are fairly expensive and probably not what they are quoting you for 5500 your boiler is as good as any out there.

I have a Weil McLain I installed in 1984 and it's still going strong.

Just a thought on what the tech found and said everything is fine.

First, your feed valve comes preset from the factory at 12psi so unless it's been shut off or manually adjusted it should never drop below 12psi so that would be a concern.

Next, your gauge not moving at all know matter what changes are made. If your relief valve blows again and the gauge still reads 12 there is a problem with the gauge and should be replaced.

Last, at 12psi you most likely will not get heat to the 3rd floor because there just is not enough pressure in the system.

Pressure is figured roughly 2 to 1. For every 1lb of pressure you will get 2ft of height so it would take at least 15psi minimum to get to the 3rd floor which we figure at 10 ft per floor. I would run about 20psi to make sure. (I'm sure somebody will comment it's 2.32 ft per lb of pressure or something like that but I just can't be bothered. 2 to 1 is close enough and you'll always have enough.)

If you are getting heat on the 3rd floor I suspect your gauge is off and there's more pressure in the system than the gauge shows.

Just curious, how did he check the expansion tank.
 
 

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