Operating scenario is following :

    You establish water teplota na a gas kotol - pre example 50 degrees. a na an elektródový kotol - 55 degrees a above, but only pri night time. As night falls, elektródový kotol "understands" that teplota is less than it was required, so it turns na a raises coolant teplota do 55 degrees. It maintains teplota till morning, a then reduces teplota do 20 degrees (pre example). All this time gas kotol was pumping water through itself by recycling čerpadlo, "thinking" that it happens by its service, that water will not get cold a that gas burners are not switched na. v morning gas kotol sees that teplota fell do 50 degrees as it was established a it gives  command do gas burners do turn na. This scenario is ideal s interval meter. v this case economic effect will be noticeable.

    Solid-fired kotly are even more simple v use. There is no need v setting teplota, because it is regulated while burning wood alebo coal (except modern solid-fired kotly s regulation air feeding damper). Simply said, solid-fired kotol works while wood alebo coal is burning. When wood is burnt, then an elektródový kotol switches na. 

   There is one minus v this scheme. Absolutely all double-circuit gas kotly works na following principle: when you start hot water v order do wash hands alebo dishes, gas kotol stops circulating čerpadlo work. flow channel v vykurovanie system stop working. An elektródový kotol continue coolant vykurovanie, but only from inside. Theoretically, water termocontroller, installed v elektródový kotol will be activated. But it may not happen pre some technical reason. v any event this variant is possible. What will happen then? pressure v system will jump a excessive water will start flow out from relief valve gas kotol. Anyway, nothing good.
    It is better not do open hot water while an elektródový kotol is working. But it is case double-circle gas kotly. It will not happen s single-circuit a solid-fired kotly due do  absense second hot water circuit.