Hi, I have noticed recently that when the central heating, set at 60, goes off the pump no longer overruns for the period of 3 minutes like it always has. Is this a problem? With the dhw it does the 1 minute overrun still.
Main combi eco 30 pump overrun
- Thread starter iceman2010
- Start date
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The pump overrun is there to get rid of residual heat when the burner goes off. If the pump stopped immediately then the residual heat from the heat exchanger would continue to heat the now static water and increase its temperature to the point of activating its overheat trip. To stop this happening, the pump runs on for awhile to get rid of the excess heat.
With some boilers this function is controlled by time, i.e. the pump runs on for a few minutes after the end of the heating cycle, with others it's controlled by temperature and the pump will run until the temperature is at a level low enough to remove the risk of tripping the overheat thermostat.
However, I'm not familiar with the inner workings of your particular boiler, but I suspect that yours may come in the latter camp and if you have lowered the heating temperature then maybe it's now low enough not to initiate the pump overrun. If as a test you ran the boiler at a higher temperature and the pump overrun operates then, I guess you have your answer. However, if it's not tripping the overheat sensor [Error code E110 - Safety Thermostat Operated] I personally can't see it being a problem.
Hopefully a Main-combi-eco expert will be along and able to confirm, or otherwise.
With some boilers this function is controlled by time, i.e. the pump runs on for a few minutes after the end of the heating cycle, with others it's controlled by temperature and the pump will run until the temperature is at a level low enough to remove the risk of tripping the overheat thermostat.
However, I'm not familiar with the inner workings of your particular boiler, but I suspect that yours may come in the latter camp and if you have lowered the heating temperature then maybe it's now low enough not to initiate the pump overrun. If as a test you ran the boiler at a higher temperature and the pump overrun operates then, I guess you have your answer. However, if it's not tripping the overheat sensor [Error code E110 - Safety Thermostat Operated] I personally can't see it being a problem.
Hopefully a Main-combi-eco expert will be along and able to confirm, or otherwise.
@gas112Hopefully a Main-combi-eco expert will be along and able to confirm, or otherwise.
. Afaik, looking in the manual, it’s the room thermostat being open allows pump overrun, but pump overrun is usually determined by the pcb.Sponsored Links
The 3 min pump overrun only happens when there is no further demand for CH, i.e. if the timer and room thermostat are still calling for heat the over run wont come in, put the CH on till the boiler fires then switch it off at the timer or turn the room thermostat right down and burner should extinguish but pump should over run for 3 mins
Thanks for replies. So historically the pump overrun has always kicked in after the CH demand has ended whether that was the room thermo or the mechanical timer. i had tested it the other day by turning down the room thermo while boiler was fired up and the pump did not overrun and likewise tested with the timer and that also did the same.
I have had the ch temp at 60 for the last 2 years and never had this issue.
After the pump stops the boiler temp does rise to about 64-65.
The manual says the pump should overrun for a period of 3 minutes after ch demand has ended and 1 minute for dhw, which still seems to be the case.
Might not be related but the issue only seems to have started since the heat plate exchanger was changed last month.
I have had the ch temp at 60 for the last 2 years and never had this issue.
After the pump stops the boiler temp does rise to about 64-65.
The manual says the pump should overrun for a period of 3 minutes after ch demand has ended and 1 minute for dhw, which still seems to be the case.
Might not be related but the issue only seems to have started since the heat plate exchanger was changed last month.
The signal for the pump over run comes from the PCB, did you get water on it when changing the plate heatexchanger
No water spillage.
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