Programmer problem
- Thread starter Bryan de
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OK remove the programmer and central heating should not work even with FCU switched on. Is that the case or not?
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With TRV's fitted there is little need for a wall thermostat, the idea is as the TRV closes it pushes more water through the valves still open until the by-pass valve opens, which results in hotter and hotter water returning to boiler which in turn modulates (turns down flame) to suit return water temperature until at minimum output at which point it start to cycle off/on slowly increasing the off time (called anti cycle software) but it can never turn off boiler completely as once that is done, it has no way to know when to turn on again.
In real terms by the time the cycling is not required, we have manually turned off the boiler. So no real need for wall hard wired on/off thermostat.
In my parents day central heating was used to warm home before you got up, or before you returned home, once up you lit a fire, suppose we still could, but too lazy to be bothered to light a fire and carry out ashes, and of course all the dusting required when using real fires.
If your programmer was working, adding a thermostat is easy, just replace with Hive, but need to get it working first.
I removed the programmer and the CH still works using the FSU
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Well, it shouldn’t, so must be getting a switched live feed from the fcu
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I agree it shouldn't but seems far more likely line feed is from the motorised valve.
Standard S Plan
So line to 1, on to grey, grey to orange, which fires boiler. The V3 micro switch
can easy stick in, so next question is when you switch on/off at the programmer does the motorised valve move? Often you can feel if the valve has opened using the bleeding lever and feel the resistance on the lever.You can't easy change the micro switch, need to change whole head, but common fault for switch to stick in.
Possibly, but, it was mentioned the head was changed along with programmer?
I would suggest you are wrong there Eric, on the need for a room stat of some sort to inhibit the heating system when the ambient means there is no demand. Lack of such a stat will mean user intervention to turn the heating off manually, when there is no need for heating - the alternative is a lot of unnecessary wasted heat and fuel, in both winter and summer.
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This leads me to look at the wiring centre, i.e some thing where a mistake could easy be made.
I am considering two faults, either the brown to motorised valve has been put in wrong hole in the wiring centre, or the motorised valve has change over contacts
and white and grey mixed up.I am assuming you have some common sense and so looking for an easy error for some one with some sense to make, rewiring a switched FCU does not seem to be some thing some one could do in error, so this points to the wiring centre, where much easier to make an error.
Today when the central heating is often the sole form of heating, and we have got use to leaving it do its own thing yes, but a modulating boiler with anti hysteresis software does not fire up for long, even my oil fired boiler with DHW with thermo syphon only runs for 20 minutes when central heating water is not circulating, so looking at a 5 - 10 minute burst every hour or so, and at minimum setting so 6 kW typical, clearly even 1 kWh a time is more than we want to waste, but unlikely a user would not turn off the system on a warm day.
Yes would want to fit thermostat, but first let us see it working, before any alterations.
post a pic of the motorised valve you mention, I think you have 2 not 1, your wiring pic isnt very clear but looks like an S PLAN so you will have 2 x motorised valves
The original installation had 2, but this was changed some time ago so now only 1.
This might be why it’s working the way it is. Can you post a photo of motorised valve and inside wiring center?
That is a total mess, your programmer is wired for S plan, which requires 2 x motorised valves, you say you only have 1 so it will never work correctly
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