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I don’t think so. As D_H states, ‘The flame can be displayed without the boiler actually being on.’ This also concurs with the Honeywell description. The thermostat sends a 0-100% demand to the receiver, not an on/off demand.

The flame symbol on the CM90x does represent relay on, however on the CM92x, it doesn't; green light on the receiver does. Quoting from the Honeywell installation guide:- ‘The receiver box receives the heat demand (0-100%) signal from the room thermostat. The room thermostat will display the...

If, with a minimum on-time of 5 minutes and a cycle rate of 6, the cycle period remained as 10 minutes, then the system output level can go no lower than 50%, which is going to be too high to maintain a set temp in most conditions. The CM control must increase the cycle period if a higher...

That’s correct, the ‘minimum on time’ is applicable when the thermostat is using time proportional control in the proportional control band (the 1.5C around the set point). If you increase the on time you are making the control mechanism coarser and the temperature will fluctuate somewhat more...

Or get rid of the old timer and fit a programmable Honeywell CM927 instead?

It is equipotential bonding, not earth bonding. The thing that makes a conductive part such as a radiator or sink potentially hazardous is that it may be electrically connected to earth via a water pipe (it is classed as an extraneous conductive part). Using plastic piping breaks this electrical...

That’s earthing (‘grounding’). This is equipotantial bonding, which serves a different purpose to earthing.

See this article for an explanation: http://www.ultimatehandyman.co.uk/EarthingPlasticPipes.pdf

I think you are quite right Matthew. The integral part of the controller positions the proportional band about the set point. D_H and I discussed this in a thread a while back. See http://www.diynot.com/forums/plumbing/honeywell-cm927-thermostat.297354/

I have been selective in my quoting of the Compliance Guide requirements to focus on room stats. The requirements of course also cover water heating zones and interlock.

Part L of Schedule 1 of the building regulations 2010 requires that ‘reasonable provision shall be made for the conservation of fuel and power by providing fixed building services that have effective controls’. Approved Document L1B describes in its General Guidance that: ‘Whenever a fixed...

Are you refering to the building regs Part L1?

You would not have used the wire on terminal 4 of the Towerstat on a DT90 because that is the neutral. I think you have got your designations wrong. See http://www.tfc-group.co.uk/assets/graphics/static/RS%20RCS%20RFS%20User%20instructions.pdf For the DT92, look at page 6, diagrams a. & c. at...

My apologies, I should not have phrased the response as I did. These are problems that I have had on a similar boiler and which were fixed by a heating engineer. I am not advocating that the OP should undertake any work on the boiler himself.

Does the fan seem to be running normally? If it is not, this can prevent the pressure switch operating correctly. Also check that the pipes connecting the pressure switch are not perished at the ends, again preventing the switch operating correctly. I have had both problems with my Baxi Solo.

If you fit a tank thermostat, you can wire the controls as shown below which will prevent the boiler cycling when there is no heating demand and the tank is up to temperature. When using HW only, the tank thermostat it will control the tank temperature. This obviously isn’t as good...

No, it doesn't matter.

Like this: http://www.honeywelluk.com/Documents/All/pdf/936.pdf

If you don’t have wiring in place for connecting a simple wired room thermostat, the easiest solution may be to use a wireless dial thermostat such as: http://www.heatingcontrolsonline.co.uk/honeywell-y6630d1007-wireless-room-thermostat-p-279.html The receiver box will simply replace the...

I am a bit confused because as far as I can tell, the HC60NG is a wireless receiver and the CM31 is a wired programmable stat. However, assuming that the HC60 was controlling your system: Connect the Brown that went to the HC60 L to the CM907 terminal ‘A’ Connect the grey that went to the...