Flow / Return Temperatures

Discussion in 'Engineers' Talk' started by Stoneyt79, Nov 30, 2021.

  1. Stoneyt79

    Stoneyt79 New Member

    Looking for an explanation as to why I have such a drop in flow and return temperatures when the boiler comes on. I have a good temperatures when the boiler is off. Is there an issue with the circulating pumps. See attached picture
     

    Attached Files:

  2. MGW

    MGW Screwfix Select

    First question is what type of boiler, my 1980's gas boiler had a Myson fan assisted radiator and the instructions wanted a high flow rate to maintain the matrix temperature with fan on full speed, and at that time it did not matter if return water was only 5°C cooler than output.

    But then we got the condensing boiler which extracted the latent heat from the flue gases, and this resulted in the TRV head becoming a must, and the lock shield valve setting becoming critical.

    I set my mothers radiators using the target and current temperatures. Flat Battery TRV.jpg If current exceeded target close the lock shield valve a bit, and it got to a point where the rooms were all spot on.

    I have not a clue what algorithms are built into her Worcester Bosch boiler, however the radiators were all running cooler once set. This had a massive change with some rooms. The living room had a massive bay window, set to 22°C before adjusting lock shield valves I would see 32°C when sun came out, clearly the sun heating the room, but radiators were hot when sun came out, so even when the TRV closed the radiator was still heating room, but once set, still over shot, can't stop sun heating room, but only 24°C as the radiators were not running as hot.

    A on/off thermostat should only switch off when warm outside, or there has been a timed reduction in temperature set. It is only there to stop boiler cycling as summer arrives, it does not set room temperatures.

    Having said that this house with oil still like 1980's house with gas, it seems oil boilers don't modulate.
     

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