Boiler pump started whirring and hot water weak

Old 03-08-17, 11:18 AM
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Boiler pump started whirring and hot water weak

Hello, first post on this forum.

I was painting my kitchen and needed to remove the radiator to access the wall behind it. I closed the valve and drained the radiator (water came out completely black and smelled kind of like antifreeze) completed the job and replaced the radiator. I opened the water intake at the boiler, filled the system to a little over 1 bar pressure, bled the radiators (none but the one I replaced had any air in them) and figured I was good to go.

But now when I turn on the hot water, the boiler pump makes a consistent whirring sound that it never did before. The boiler kicks on the flames as usual (although the hot water is not as hot as before) and this sound from the pump continues until I turn off the hot water at the tap. This does not happen if I turn on only cold water. After the pump shuts off, I can hear a faint gurgling in the boiler for a couple seconds.

I bled the pump, thinking there might have been air in it, no dice. I don't want to burn out the pump or something, so I'm afraid to use the hot water. What is this sound?

Thanks for any tips. My boiler is a Vaillant Thermotop pro. I'm including a picture of the pump.
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Old 03-08-17, 12:48 PM
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Okay, the pump eventually quit making this noise after the thermostat kicked on and the boiler ran for awhile. I'm guessing there was air somewhere in the system and the pump had to run for awhile to fill the circuit with water, but I don't know. I'd still like to know what the noise was and where I went wrong since I bled all the radiators and it still acted funny. Thanks.
Old 03-08-17, 02:11 PM
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Post a video with sound when the pump makes the noise.

The black water you encountered is harmless and is inevitable in a closed hydronic system with ferrous materials. Bleeding and flushing is useless - the black color will promptly return.
Old 03-08-17, 02:28 PM
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Welcome to the forums.

Normally the circulation pump is not affected by domestic hot water use.

We don't know much about your system. It sounds like you get your DHW from the boiler. Is that from just a tankless coil or do you have some time of water storage tank ?

Just one pump ?
Possibly zone valves ?

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