Can any one help? I have just had fitted a new boiler with a programmable thermostat. I am not convinced that it has been wired correctly. When the thermostat reaches temperature it turns OFF the CH valve and goes via the pump overrun pipe work. Surely the boiler should just turn off its gas heating and the central heating pump run normally and the CH motorized valve stay open. At the moment the poor CH valve is activate every time the thermostat clicks on or off. Is this correct? Thanks Spike123
Honeywell Prog Thermostat
- Thread starter spike123
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Thanks very much, so the CH valve should be closed every time the thermostat clicks OFF and the CH valve should be driven open when the thermostat demands heat. Are my honeywell motorizied valves rated for lots of on and offs. I thought the CH valve would stay open while the CH is ON, and the thermostat just controls the boilers gas/heat. The thermostat cycles alot, say every minuet , hence my concern for my motorized valve. The old boiler did'nt work in this way?
I am an electrician.
Im sure the valve can be opened and closed quite a few times!, and yes your old system was probably plumbed slightly differently.
The thermostat calls for heat, the valve opens, which tells the boiler to fire.
Once the room has reached temperature it works in reverse to above.
Im sure the valve can be opened and closed quite a few times!, and yes your old system was probably plumbed slightly differently.
The thermostat calls for heat, the valve opens, which tells the boiler to fire.
Once the room has reached temperature it works in reverse to above.
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Presumably you have a second valve in the hot water circuit. If the valves are opened when CH or HW went ON and closed when they got OFF, there will be no way of controlling the temperature when both are ON at the same time. Even if one thermostat says the CH or HW is up to temperature, water will still continue to circulate because the valve is open.
Thanks very much for your reply. What i have found is that the position of the Honeywell Prog thermostat (In the Hallway) nr a radiator (which i have even turned off) and yet still hunts between being on and then off in the space of a minuet or so. This means the boiler,pump and valves are working hard. This never happened with my old boiler/thermostat. whats needed is some hysteresis in the Honeywell thermostat so the toggling action I get now will reduce. I have spoken to the plumber who fitted a second honeywell prog stat and this behaved the same.
I re wired my old stat (Lyndis Gyre) in and it also would switch on and off at a similar rate. I guess i just have to move the position of the thermostat, which is a pain as its a re wire. I have considered getting a wireless unit,but these need a permanent Neutral and live feed, which i don't have at the current position,just a Neutral, live in, and switched live
BLUE,RED and Yellow). Any advice is welcome. Spike 123
OK so you don't have a wireless stat, so it can't be communication problems.
Which Honeywell thermostat do you have?
Which make and model boiler do you have?
Can't see the problem. That's all you need for a wireless stat.
On the Honeywell programmable thermostats, such as the CM907, the cycle rate of the thermostat, once it is up to temperature, is a system parameter that can be changed. The default setting is 6 cycles of 1 minute per hour, so it is probably operating normally.
My boiler is a Viessmann 26Kw open vented system
The main controller is a Honeywell ST9400c with a Honeywell CM907 programmable thermostat. Its running with the CH on continuous and the programmable thermostat is controlling the CH. It all works fine until it reaches temperature. Then it seems to cycle , by turning the CH on and off within minuets of doing one or the other. Can you suggest any solutions? Many thanks
OK, so can i change the cycle rate to do less 1 minuet cycles per hour, how is this done? The manual does not explain how to change this parameter.
Thanks for your advice
This is described in the Product Specification sheet which is available here:
http://www.uk-plumbing.com/brochure/honeywell/CM907Data.pdf
I think you can only reduce the cycle rate to a minimum of 3 per hour, you can't disable it completely. However, you can also increase the time that it is on for. So you could try 3 cycles of 2 minutes per hour. The idea is that it keeps the system ticking over and maintaining the set temperature.
http://www.uk-plumbing.com/brochure/honeywell/CM907Data.pdf
I think you can only reduce the cycle rate to a minimum of 3 per hour, you can't disable it completely. However, you can also increase the time that it is on for. So you could try 3 cycles of 2 minutes per hour. The idea is that it keeps the system ticking over and maintaining the set temperature.
That's not correct. The standard setting for gas boilers is six cycles per hour, i.e. six periods of a ten minute period. During each ten minute period the ON time depends on the temperature deviation from the set temperature. There is however a Minimum ON Time of one minute. This is called PI control.
Some time a go I read that Danfoss said that PI control should be turned off if motorized valves are used. I wrote to them and asked why this was. Here is their reply:
When the thermostat is using the chrono feature (PI logic) it breaks the boiler firing time into defined lengths of time. Set to chrono six mean that it will fire the heat source up to six times an hour, breaking an hour into ten minute segments. Simplistically speaking there could be five minutes on and then five minutes off. It is self adjusting, so if it hit its desired temperature it would turn off and it would reduce the on period. And if it did not hit its desired setting it would increase the on period, Say to eight minutes on and two minutes off. Now as the room gets close to the set temperature it could be on for a minute. Now motorised valve take time to activate ours take approximately twenty seven second some others may be longer, this could cause the boiler which would be switch by the valve to be on for a very short time less than thirty second which they believe may not be good for the actuator or boiler.
The Honeywell CM907 does not have a facility to switch off the PI control, so it might be worthwhile talking to their technical department about your concerns. Tel 08457 678999.
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