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Expansion tank

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  • 09-11-2020 9:10pm
    #1
    Takestan
    Registered Users Posts: 32 ✭


    My central heating system consists of oil burner and solid fuel, I have a 1000 ltr hot tank The other night I noticed the expansion tank water was very hot
    The stove was lit at the time and possibly the heat was on or just after going off.
    Is this normal ?? seems strange to be heating the expansion tank.
    The expansion tank is a small black open tank with water I presume it's an open system


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    #2
    John.G
    Registered Users Posts: 3,476 ✭✭✭John.G


    Is that 1000 litre tank heated by two separate coils or is there say one coil heated by the oil fired boiler but the stove heats the water directly in that 1000 litre store?.


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    #3
    Takestan
    Registered Users Posts: 32 ✭Takestan


    John.G wrote: »
    Is that 1000 litre tank heated by two separate coils or is there say one coil heated by the oil fired boiler but the stove heats the water directly in that 1000 litre store?.

    I wouldn't be 100% sure but as far as I know it's a triple coil tank the solar panels been the third


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    #4
    John.G
    Registered Users Posts: 3,476 ✭✭✭John.G


    OK, that makes sense so that expansion tank probably serves both the oil fired and solid fuel boilers, you should see two vents to this tank, when the stove is on, see if hot water is coming out of one, also check that the solid fuel circ pump is running normally and starting/stopping on its pipe stat. Has this circ pump been renewed recently/.


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    #5
    Takestan
    Registered Users Posts: 32 ✭Takestan


    John.G wrote: »
    OK, that makes sense so that expansion tank probably serves both the oil fired and solid fuel boilers, you should see two vents to this tank, when the stove is on, see if hot water is coming out of one, also check that the solid fuel circ pump is running normally and starting/stopping on its pipe stat. Has this circ pump been renewed recently/.
    Will check that out the vents and pump to morrow
    no same circ pump this 15 years


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    #6
    Takestan
    Registered Users Posts: 32 ✭Takestan


    John.G wrote: »
    OK, that makes sense so that expansion tank probably serves both the oil fired and solid fuel boilers, you should see two vents to this tank, when the stove is on, see if hot water is coming out of one, also check that the solid fuel circ pump is running normally and starting/stopping on its pipe stat. Has this circ pump been renewed recently/.
    There is 2 vents alright looks like it's the vent from the oil burner circ pump is cutting in at 50 degrees not sure what proper cut in temperature


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    #7
    John.G
    Registered Users Posts: 3,476 ✭✭✭John.G


    50C cut in should be OK, can you confirm that the vent is only "pitching" (water flowing from it) if that's what's happening with the pump on or off.
    Is the stove just heating this 1000 lire tank and nothing else?


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    #8
    Takestan
    Registered Users Posts: 32 ✭Takestan


    John.G wrote: »
    50C cut in should be OK, can you confirm that the vent is only "pitching" (water flowing from it) if that's what's happening with the pump on or off.
    Is the stove just heating this 1000 lire tank and nothing else?

    Yes there is water flowing from the vent pipe into the expansion tank from the stove and the cir pump was on
    The stove is plumbed as a secondary system to the rads and it's this circ pump than is running


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    #9
    John.G
    Registered Users Posts: 3,476 ✭✭✭John.G


    I don't understand the reason for that 1000 litre hot water store if the rads are being heated directly from the stove via its circ pump, I assume the stove can circulate water through its coil in the store by gravity flow. You should try and see where that Vent is Teed off from the system and where the cold feed from that small feed&expansion tank is teed into the stove system, there may be a partial blockage there but without some form of drawing/sketch its hard to comment on what the problem is.

    I also misread your post #6 as I thought it was the stove circ pump that was being started by the pipe stat, a oil fired boiler circ pump is not controlled by a temperature stat, when the oil fired boiler is called in by a programmer/roomstat /cylinder or store stat. the circ pump will run continuously until no further demand, so too will the boiler but the burner will cut in/out on the boiler stat, also a boiler (burner) stat set point is its cut out temperature, if set to say 50C, it will cut in at ~ 40C, a stove stat works differently, it will start its circ pump at its stat set point temp and cut out ~ 5C lower so if set to 50c it will start the pump at 50C and stop it at ~ 45C.


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