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B Shower at times gets cold

  1. Nov 11, 2016 #1
    If I turn up thermostat to 70, the rooms get warm. I notice shower head gives warmer water at this temperature. If I turn thermostat lower, the rooms get cooler as it should be. Again I notice shower gives less warm water. What is the connection? Or is it coincidental? It happens too often that there may be a connection.

    I ask this cuz I am aware that thermostat deals only with air. Not water.
     
  2. jcsd
  3. Nov 11, 2016 #2

    Drakkith

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    Perhaps your pipes aren't as insulated as they should be?
     
  4. Nov 12, 2016 #3
     
  5. Nov 12, 2016 #4

    sophiecentaur

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    Two effects coinciding, I suggest: If the temperature control on the shower is not too good (and they can be poor) then the final water temperature could maybe not be independent of the hot water temperature. Also, it is not uncommon to find that the thermostatic control of the hot water supply is not too good and, with the room thermostat turned high, the boiler runs for longer per hour (to feed the radiators more). That could result in more heating water is getting into the hot water tank and raising the hot water temperature. I have definitely experienced domestic hot water temperature going up when the boiler runs more.
    To sum up: two imperfect feedback / control systems are allowing the overall output value to vary when it shouldn't.
    Perhaps you could measure the temperature of your hot water as the boiler duty cycle changes.??
     
  6. Nov 12, 2016 #5
    Beyond my grasp. When you say thermometer control of the shower, I guess you mean the dial knob that use my hand. You are right about the feed to radiators. It has hot water pipe with fins inside the radiator. More question: does shower share the same water tank as the radiator pipes. Maybe. But when water leaves water tank to boiler. It has separate pipes. One to radiator and one to shower. I am assuming shower has its own separate thermostat hooked to the dial knob. Also the wall thermostat for radiators.
     
  7. Nov 12, 2016 #6

    sophiecentaur

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    Most systems have common hot water fed to the radiators and to a heat exchanger in the 'hot tank' (if they are not 'combo' systems) with a valve to push the boiler water to one, the other or both.. There is a thermostat in the boiler that keeps the water through the boiler at a pre-set temperature (when the boiler and pump are running). There is also a 'tank thermostat' which lets water into the hot tank heat exchanger when needed. The temperature of the water in the hot tank should be kept at the setting of that thermostat but it seems to be affected by how long the boiler is supplying the rads. I always reckon that there changeover valve is not perfect. It could also be affected by how well the heat exchanger in the tank works. Bottom line is that I think the tank water is actually heated more when the boiler is on a lot (for the rads). What happens in the shower control will depend on how well it can control the temperature by mixing hot and cold. (Possibly not very well) So the water from the head will not be the same temperature but be affected by the hot tank temperature. So two controls are operating in tandem. If they were perfect, the shower temperature would be constant - but they, apparently ain't!
     
  8. Nov 12, 2016 #7
    Sophiecentaur,

    Thank for the explanation. I will read again a few more times. Interesting.
    Thank for the tips.

    Alan
     
  9. Nov 12, 2016 #8
    When you say hot water tank, do you refer to water expansion tank?
     
  10. Nov 13, 2016 #9

    sophiecentaur

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    You need to give me some help here. I don't know whether or not your system has a hot tank(=hot water storage tank). Did you think to google Domestic Hot Water Systems? There are a million images to pick from to find one like yours.
    I wonder why you asked the original question. There's no way anyone could say "turn lever x and it will be sorted" without some adequate description of your system.
     
  11. Nov 13, 2016 #10
    Oh I see. I just googled and now know what a water tank looks like. I will take picture tonite or tomorrow and forward it. I did not know that the tank can hold hot water.
    By now I gave you big help. Thanks. You huge help!
     
  12. Nov 13, 2016 #11

    CWatters

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    Does the tank have a thermostat on it? If so then its a hot tank or thermal store. Otherwise it could be a cold water tank.

    How many pipes go in and out of the boiler/furnace? Two or three usually.

    Somewhere there is usually a valve that switches the hot flow from the boiler to either the hot water system or the heating system. If that has a fault which prevents it switching over to the heating fully then that could cause the problem.

    Are there any overflow pipes on the outside of the house and are they leaking water? If yes and that water is warm that could point to a fault in the heat exchanger in the hot water tank.

    The are probably many other possible causes.
     
  13. Nov 13, 2016 #12
    You ask many good questions. Interesting. I will try to answer by Wednesday if not Tuesday evening with picture of the water tank.
     
  14. Nov 13, 2016 #13

    sophiecentaur

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    I don't think this is exactly a 'fault' condition - just poor temperature regulation in the system. I think that the tank thermostat system is probably responsible. It measures the temperature of the side of the tank, about 1/3 of the way up from the bottom. It knows nothing of the distribution or circulation of the warming water in the tank and the very crude heat exchanger (a simple coil) will perform differently as the heating water temperature varies. When the rads are on, the boiler water will be hotter when the valve starts to deliver to the hot tank. Simple control theory doesn't account for this sort of thing - it assumes that a thermostat always does its job and that it will produce the same result always. I fought several incarnations of my last heating system and gave up fooling around with the tank stat. It just seems to do what it likes.
    If the OP has a system like mine plus an inadequate shower stat, it doesn't surprise me that he gets the results he does.
    I Could suggest that althepump makes a note of the actual hot water (wash basin) variations when the rads are on and off. If it varies a lot then I reckon that's his problem. Also, what is the effect of flushing the lavatory or turning on bath taps etc. That would test how good the shower stat is - some of them are rubbishy and some are very good.
     
  15. Nov 20, 2016 #14
    IMG_0118.JPG IMG_0118.JPG IMG_0119.JPG
     
  16. Nov 20, 2016 #15

    sophiecentaur

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    You have completely flummoxed me now. That picture seems to be of a water softener. It should never get hot because it's fed with cold water.
    Also, you seems to have quoted CWatters twice and mad no comment.
    You could find yourself in hot water with mods for this.
     
  17. Nov 20, 2016 #16
    Sophiecentaur,

    First thank you for pointing out it is water softener. It's.

    I tried to delete CWatters w/o comment, but I could not. I will have to figure it out tonight.
     
  18. Nov 20, 2016 #17
    Second note: I don't know how these CWatters w/o comments get there. It must have happened when I upload pictures of the water softener.
    I must have done something wrong. I hope the mods can just delete the #14 posting quickly. Or just the whole topic to make it look less messy!
    I just could not delete them. Thank you for making this notice.
     
  19. Nov 20, 2016 #18
    Thank again for identifying the water softener. It appears I don't have water tank at all. Hope mods will delete #14 posting soon.
     
  20. Nov 21, 2016 #19

    sophiecentaur

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    So your boiler will be a 'combo', which turns on on-demand when you require hot water (?). That would be an easy thing to check- stand by the boiler and ask someone to run the shower for a minute or two, with the CH turned off.
    There are several different designs of combi circuits. Normal combi boilers (link which you must look at!!) do not heat the hot water directly but pass boiler water through a high capacity heat exchanger which is in the boiler itself. I suspect that, when the CH is in operation, the heating water may be hotter because the boiler gets cranked up higher with the flame modulator. So the supply to the HW heat exchanger will be a bit hotter - giving you hotter hot water. It could be a slight fault in the boiler.
    Nevertheless, it still looks to me that the shower thermostat is not very good. AS I mentioned before, that can be checked by standing in the shower and getting someone to flush the loo and turn on cold taps fully. If you leap out of the shower, the stat isn't working too well.
     
  21. Nov 21, 2016 #20
    I think I know how it happened. I did add comments wth same font size
    Quoted "which turns on on-demand when you require hot water" is an excellent reply! It is exactly what is happening every time I turn on the shower. I always have to wait a full minute or two before I feel warm/hot water. I am still trying to figure out what CH is.
     
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