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Yes it is the time proportional output control that makes the boiler fire so regularly. By default the DT90 is set to 6 cycles per hour so you should find that it fires no more than this and sometimes less. The thermostat is not switching so regularly because it is sensitive, but because it is...

If it is the Time Proportional control that you don’t like then the option to turn it off may be attractive. An argument put forward for TPI is that, because it operates the boiler in regular short bursts, the water temperature remains relatively low (as you note), and therefore the efficiency...

Many boiler installation manuals specify the use of heat resistant cable. For example, from a Viessman manual: ‘The mains cable must be at least 0.75 mm2 (24/0.2 mm) PVC insulated to BS 6500 table 16.’

Only if it has an optimum start function. The Honeywell CM907 does, but some others do not.

How are the boiler and pump in the primary circuit controlled? In my thermal store system the boiler and pump are simply controlled by the tank thermostat. The boiler fires to bring the tank back up to the temperature set on the tank, so it always recovers to the set temperature; although this...

Yes you need a battery powered unit. I would also recommend the CM907. I would say it is easy to programme once you have spent a little time understanding its functions, maintains temperature very accurately and of course you have the advantages of setting temperatures through the day and week...

For a combi, use a Honeywell CM927 programmable wireless thermostat; then you don't need a timer.

To save energy, which seemed to be your primary concern? I have a 1200 x 500 radiator heated electrically in the summer with a 150W element. It is on for two 5 hour periods a day which works for drying towels. Not sure what you mean by the standard 65C - do you mean the temperature it would...

You don’t need to have the heater on 24/7. You can connect it via a time controller such as http://www.tlc-direct.co.uk/Main_Index/Timers_Index/Immersion_Heater_Timers_1/index.html Using time control and a thermostatically controlled element will greatly reduce the energy use.

The FAQ gives a method of measuring the rate of use of gas in KW. If you just want to know how much you have used between two readings: If your meter measures in cu ft, multiply the total used by 0.317 to give KW hours. If your meter measures in 100s of cu ft, multiply the total used by 31.7...

Did he not install a new thermostat?

Have you tried removing then replacing the batteries?

You’re right. However, the ‘digital’ DT90 does not exhibit hysteresis because it uses a different control method (self-learning ‘fuzzy logic’ time-proportional control algorithm). That may certainly help, although the position of the thermostat may also be a problem. Using the wireless version...

That is as recommended by Honeywell for an oil boiler in the spec sheet for the DT92. See: http://www.honeywelluk.com/Documents/Full-Specification/pdf/1077.pdf Only increase the bandwidth if you are getting overshoot in temperature following a warm-up period.

You should be able to connect a ‘master thermostat’ in parallel with your programmer CH output so that when the temperature drops below the set-back level it will turn on all zones. This will operate at all times effectively like a frost thermostat so would also be useful for maintaining a...

If you connected neutral to earth, you would expect an RCD or RCBO to trip, which it sounds like it did. With a digital stat that does not require a neutral, you would expect to connect to the brown (live) and brown sleeved (switched live) wires only. Are you saying that did not work?

That's quite normal when using a programmable stat. See below, taken from a Honeywell guide: