cycle rate and minimum on

[tdemeyer]

Hi,

Excuse me for my poor english, it's not my native language..

I think we have a pretty basic boiler setup: It's a cast-iron floor standing model. When the thermostat relay closes, it starts the boiler's circulation pump, and starts to heat up the water to the max temperature set on the boiler.. When the thermostat switches off, a timer relay continues to run the pump for approx 15 minutes (but the gas is cut).

We replaced the old thermostat with an Evohome Wifi system and HR92 valves on all the important radiators (our storage room has kept the old thermostatic valve, set to a minimum temp. We don't care if it's heated or not...)

So far so good, everything is set up and seems to work fine.

When the room is nicely heated up, I notice the boiler is still switched on every 10 minutes, for approximatly 1 minute. So I presume this is related to the 6 Cycles/1 minute minimum parameters that are set in the system menu of the controller.

Can someone explain me whet's the purpose of these cycles? Am I correct in thinking it's used to keep the water in the system at a reasonable temperature, so it's ready when any radiator valve is 'asking for heat''?
If this is correct: Given the fact that in a heated house all radiator valves are closed, and therefore the heated water is only running in bypass through my boiler: would it be better to change the cycle rate to al lower number? (saving extra gas, but also making sure the circulation pump lives longer by not having to overcome the extra pressure needed to trigger the bypass valve)

Tim

[Richard]

Hi Tim,

The cycle rate and minimum on time defines how the evohome system handles the heating appliance in time. If the heating appliance can handle it, the more cycles and less time it is on will ensure greater accuracy of the temperature control.

Modern gas boilers can easily handle 6 cycles per hour and 1 minute minimum on time, where a cast iron gas boiler would take a bit longer to heat up and be useful, so maybe 6 cycles per hour and a minimum run time of 3 minutes?

When there is no BDR91 demand, the boiler an pump will be off (no water running anywhere).

I hope that helps.

Richard

[Force8]

Follow on question... I have searched extensively for information on appropriate cycle and minimum run times for an oil-fired boiler and found nothing of any help. So, can you make any suggestion on appropriate settings..?

[Richard]

Oil boilers should be set to 3 cycles an hour and 4-5 minute minimum on time, as per the decent technical guidance Honeywell used to give with their CM series products - https://heatingcontrols.honeywellhome.c ... f/1066.pdf

cm700-technical-details.JPG (133.22 KiB) Viewed 984 times

[Bart]

The boiler cycles when the room is at setpoint, so that the temperature remains at setpoint.
There is always a loss of energy through windows, doors, walls, so in order to keep the room temperature constant, some heat is required to compensate these losses. You should notice that the radiators remain warm in this situation.

[neugen]

Hello,

When using Evohome with the Openthem bridge, are these two parameters ignored ?

Thank you.