Most efficient way to use underfloor heating?

Riablo

Have just moved house to a renovated barn in France. We are renting the property for 3 years and want to try to cut fuel bills as much as possible.

The house has solid walls approx 2 foot wide, double glazed windows etc and scored well on the energy performance certificate.

We have underfloor heating which is powered by a condenser boiler and controlled by an outside thermostat. As I understand it the flow of hot water into the pipes is controlled by the thermostat and the colder it is outside the more water will be allowed through the pipes to try to maintain a constant temperature inside the house. We control the actual temperature of the water by increasing or decreasing the temperature of the water at the boiler.

We have tried turning heating down or off during the day and then turning on or up when we are home int eh evenings but it seems to take too long for us to feel any difference. So at the moment we have the heating on all the time with a water flow of between 35 degrees and 40 degrees although this can still leave the house feeling chilly.

As the flow is controlled by the outside thermostat I am concerned that we will be heating the house more at night, when (if we had radiators) we would not have the heating on at all. We have asked the landlord for an internal thermostat so the system will adjust by the temperature in the house but so far he hasn't got back to us on this (language is a bit of a barrier so have to go through a ,middle man) Not sure if an internal thermostat would help with this kind of heating or would be compatible with what we already have in place.

We have a 1100 litre gas tank and after only a couple of months we have used 40% of the gas. We have been quoted 1700 euros (incl VAT) to fill the tank so I am really worried that this heating is going to end up costing a fortune.

We also have two hot water tanks. One connected to the central heating boiler which is currently on all the time on a thermostat. I am concerned that even with the thermostat we will be paying a lot to heat this water. There is no timer switch so no way to turn it on so it is warm ready for our morning showers. (Whenever I have had a hot water tank in the past there has been a timer and an immersion heater so we have used the timer to have water ready for morning showers and the immersion heater as required).

Second tank is electric and heats the water for the kitchen. Washing machine only has cold water inlet so hot water is only being used for hand washing and washing up. Thinking of turning this boiler off completely and boiling a kettle for washing up, although not sure really how much energy a small electric tank will use if kept on all the time.

At our old house we used to run our radiators on a timer and with a room thermostat as well as thermostatic valves and only had the heating on in the morning and the evenings when we were at home. We also had a combi boiler so only heated the hot water we needed. It was a very cheap way for us to heat our home and we were using about £65 a month gas and electricity averaged over the year.

Anyone any ideas how we can use the system at our new house more efficiently and try to cut the cost of bills.

Many thanks