programmer mode options

[greco77]

I think this may be a slightly left-field sort of question and it relates to programmer modes or types.

From what I understand, there are basically 2 types of programmers i.e. (1) basic on/off on a set temperature keeping the boiler and pump running until the set point has been reached and (2)the second type like a Digistat +3 that uses some sort of pulse modulation by checking the temperature every 15 minutes and determining of the heating should run and also dynamically adjusting the boiler run time based on the deviation between the set temperature and actual temperature. I tried one of the second type, since I thought the concept was brilliant but it did not work out as I expected. The programmer would trigger the boiler to run ever 15 minutes but only for between 2 and 5 minutes and with the delay in my boiler firing (Glow Worm Ultracom 30hxi) and the time for the water to heat and then circulate through to a 4/5 bedroom house, in very cold conditions it took for ever for the temperature to rise. I know that Drayton have since modified the +3 so that it can run in pulse mode or on/off mode.

One of the other drawbacks is that none of the events are configurable i.e. the 15 mins or the run time.

I eventually replaced it with a Centaurstat

Sorry this is a little long winded. Are there any other programmers on the market that that operate similar to type (2) above that you would be willing to recommend or have experience of?

thanks

 

[D_Hailsham]

I tried one of the second type, since I thought the concept was brilliant but it did not work out as I expected. The programmer would trigger the boiler to run ever 15 minutes but only for between 2 and 5 minutes and with the delay in my boiler firing (Glow Worm Ultracom 30hxi) and the time for the water to heat and then circulate through to a 4/5 bedroom house, in very cold conditions it took for ever for the temperature to rise.

Which thermostat did you try out?

As you have a heat only boiler, you must have a motorized valve which will be controlled by the thermostat. When the ON periods of the thermostat are very short it is possible for the valve not to respond quickly enough, so the boiler never fires up before the thermostat turns the boiler off. This will depend on the time it takes for the valve to move over. Some TPI thermostats allow you to set the minimum on time, so you may be able to compensate for the "slow" valve.

I have had a Honeywell CM927 for over three years in a Y plan system and never had the problem you described. The minimum ON time is the default one minute. I might experiment and see what the effect is of raising it to two minutes.