same rad hot one day cold the next

Aidan (UK)

Balancing?

A demand for heat on the lower floors is robbing all the water flow from the upper floor. Try partially shutting the radiator valves on the lower floors to confirm this. Keep a record of the position of the valves. Usually there's one wheel-head rad valve or TRV for the Users & one lock-shield valve for the installer to balance flow rates around the system.

John_107

same rad hot one day cold the next

We have a older 3 storey home that the 3rd floor rads are stone cold one day warm another and then so hot they have to open windows.System pressure is 18-20 psi.When rads are blead we only get water no air.One of our service guys think there could be debris moving around.I'm not convinced that's it.It must be pressure related but what's the fix?

ed wallace

rads hot and cold

your expansion tank needs draining have them do it while burner is off

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Steamhead (in transit)

Could also be

erratic circulation. Is there a pump that moves the water thru this system? If so, can you verify that it's working?

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John_107

Yes there is a 15-42 pump installed,I was thinking if we changed it to a 26-64 but that does not explain why we sometimes have heat to the rad and sometimes stone cold.It also has a Et-60 installed so draining the tank isn't the answer.By the way we are the ones servicing this home.
Thanks for your input.I'm leaning towards changing the pump

ScottMP

Ed

Please explain your thoughts on the expansion tank being the cause of this problem.

Thanks Scott

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Brad White_42

Gut check and random thoughts

Older home leads me to think converted gravity hot water. Without knowing the system capacity I cannot speak to the pump size, but if converted gravity (large pipes) the pressure gradient across the piping should not be much at all.

My thoughts still go to flow not pressure. This only occurs on the top floor and debris may be yet an issue. The shifting back and forth is naturally quite a puzzle.

Top floors in gravity HW tended to heat faster due to stack effect. Top floor radiators often had orifice restrictors which may still be in place. Easy to plug and when this happens, flow goes somewhere else... raising pressure on the other side, and back she goes. Wild guess but all I have to go on.

Might this be a top-down feed? Main riser to the attic or third floor then downfeeding all the radiators? That way any air may be at the top of the mains and would not show up in the radiators.

Off to my train- will have to think more about this. Can you post a diagram?

Brad

ed wallace

hot and cold rad

If expansion tank is full air has to go somewhere so it goes to radiators if when bleeding rads and you get water the rads not air bound drain expansion tank or check the air charge in the pressurised expansion tank

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