Control question

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Control question

Post  cactusbob on Sun Jul 21, 2013 3:25 am

In an effort to minimise gas usage in the summer I have rewired the clock on the BM2000 to control the HW rather than the heating. The heating is now set to permanently on (controlled by a programmable room stat).

This works great with it only heating the water in the morning and in the evening just before its required.

My question is what will happen when the heating is needed? Will I need to flip the switch on the BM to always on to ensure the store temp is high enough for the hot water, or will it automatically fire the boiler if required even if it is not during a HW "on" time period?

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Re: Control question

Post  southern nrg on Sun Jul 21, 2013 4:56 am

is your gas usage excessive then? the BM is designed to call for heat when the store temp goes below a certain temp 65oC I think. if it is constantly calling maybe a sensor fault. the thermal stores are designed to be efficient so once up to temp they don't require a lot of heating and therefore use minimal gas anyway. its probably less efficient if your depleting the hot water only to have to heat the whole thing again. With regards to the heating the pump which drives the heating is a separate circuit, although when heating is on it heats the thermal store for hot water as well. i'm assuming you now have 2 programmable thermostats???? or have you wired the thermostat into the hot water? I don't know how it will affect your system in the long run but obviously these things are designed by experts to run as efficiently as poss out the box.
hope that helps a little, without seeing your installation I cant comment on how you've wired it and if the heating will work.

simon
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Re: Control question

Post  cactusbob on Sun Jul 21, 2013 6:11 am

Not excessive no, but sitting out here on the patio and hearing the boiler firing up at midday for 15-20 minutes whilst knowing that no water will be needed until the evening just seems as little pointless. As does knowing that in the morning the system can quite happily manage at least a couple of showers on the stored water.

I have wired the mechanical clock on the BM to the hot water. The CH is wired to always on, but controlled by the roomstat.

I can only assume that the boiler is firing during the day to maintain the store temperature. At the moment its 45 degrees in there, after two showers this morning


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Re: Control question

Post  scorp on Mon Jul 22, 2013 3:15 pm

Cactusbob, I did nearly the same(have two timers) and it really saved me money. As for your question, when your room thermostat switches on heating, the HW timer technically doesn't need to be on as long as temperature in the tank is high enough. As soon as it drops below 65C heating will be off even though thermostat is on. That's why I put second timer and when I need CH I switch them both on plus room thermostat does the job.

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