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The extraneous conductive parts must also be bonded to the CPCs (Earths) of each circuit supplying Class 1 and Class 2 equipment in the bathroom. For a wholly plastic piped installation, it is still necessary to bond together the CPCs. See...

Once it is up to temperature the thermostat is trying to achieve a constant average output of the heating system in order to maintain the target temperature. It does this by cycling the system on and off as you have observed so that the average (Time Proportional) output is constant. Over time...

No you can’t turn off the TPI function because that is what makes it work as a temperature controller. You can alter some of the settings that affect its operation, but it depends what you are trying to achieve. If you want the boiler to fire less often, you can reduce the cycle rate to 3 per...

No, although the proportional band is a selectable parameter on the Honeywell controllers, so I would think that it is a fixed value. If it was a value that the controller determined for itself, there would be no point in it being user selectable. The Honeywell specification for the CM907...

It would be possible to do what you suggest, but you are then using the integral action to change the proportional gain of the system which will then affect the dynamic response. This would not normally be desirable.

The slope of the proportional band is effectively the gain of the proportional term of the controller. So with a proportional band of 1.5°C, the gain is 66% change in output per °C of error. When changing the proportional band parameter, you are changing the proportional gain of the control...

I think you are not accounting for the integral action of the controller. The proportional band will not normally be entirely below the set temperature, but around it. Referring to the diagram, in this example the controller is initially set up so that the target temperature Ts is at...

In mild weather, when the heat demand required to maintain the internal temperature is low, the system will be operating at the top of the proportional band, close to zero output. If the unit always uses a 1 minute minimum on-time and 6 cycles per hour, the minimum output it can use is 10%. If...

No, there isn’t a constant output, but the time averaged output of the system when working in time proportional mode can be constant. To look at it another way, in steady state conditions, the amount of energy put into the building per hour is constant and therefore the temperature is constant...

The optimisation function is well worth using but, as D_H has pointed out, it won’t affect the temperature control. It is a separate function that calculates what time to start a heating period to achieve a certain temperature by a certain time.

If, when actual is the same as target, the boiler is off permanently, then the set-point will not be maintained; the temperature will start to drop. The TPI controller works to achieve the output required to maintain the target temperature, which is when system heat output is equal to the heat...

I have never seen an explanation of actually what it does when the output demand is low, but from monitoring my own CM907 it is clear that, with a low demand, the output will stay off for a considerable time, so it is either skipping a TP cycle or using a variable cycle period. Or maybe it drops...

Yes, have a look at the Installer mode set-up in the Installation guide: http://www.honeywelluk.com/Documents/Full-Install/pdf/1069.pdf

The CM927 isn’t a conventional on-off thermostat and does not exhibit a switching differential as such. It uses Time Proportional control of the heating system to achieve a stable temperature. Around the set point temperature, the controller determines the % of system heat output required to...

Either way round.

I expect that the T6360 wouldn’t work very well because you have no neutral connection going to it to allow the anticipator to function. You can simply connect the brown and blue wires to A and B on the CM901 and you should get a much improved temperature control.

I just checked on my boiler. The switch is at bottom rear right hand corner behind the gas valve. The diagram is supposed to be a cut-away view through the boiler - not very obvious.

I had the same problem with a 50/4 boiler. The end of one of the tubes going to the pressure switch had perished so was no longer air tight and thus the switch wasn’t operating. Solved by cutting 10mm off the end of the tube and pushing it back on. I can't remember whether the problem was at the...

Yes, if you just want the system on twice a day like a conventional programer, disable periods 3 and 4. At any time that the unit is in Auto mode, if you simply turn up the temperature it will stay at that level until it changes at the next programmed time period. The idea with a...