Y Plan central heating circuit

Just been called to my daughter's house as she switched the central heating back on and the heating part is not functioning.
Does the Y Plan have a three positon valve ? Anyway this system seems to have just a 2 way valve which I can latch into the heating position manually and then the hot water controller fires the boiler and distributes heat to the central heating circuit.
I can just about hear the central heating thermostat click but that doesn't fire the boiler. So does the 2 way valve have to be motored over to the central heating position and that is what triggers the boiler?
AJH
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On 19/11/2018 18:14, AJH wrote:

A Y-Plan system does have a 3-port valve - but if you only have 2-Port valves, it ain't Y-Plan - more likely S-Plan. Is there another 2-port valve for the hot water?
S-Plan relies on the valve being fully open to operate the micro-switches which cause the boiler to fire. Opening the valve with the manual lever opens it far enough for water to flow but not enough to operate the switches. With the valve held open in this way, the radiators will get hot if the boiler is being fired by the HW circuit - as you have found, but not otherwise.
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wrote:

No so I guess it's a 3 port diverter valve and W plan.
AJH
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On 19/11/2018 20:16, AJH wrote:

Assuming it is a W plan, can't you swap the priority at the programmer? - at least as a diagnostic step. It may help confirm what is going on. If the heating now works but not the water, the valve is moving and you need to look elsewhere. If there is an electric immersion heater, she could use that until you can fixed things- assuming the heating works.
Changing from W to Y is just a wiring change and probably worth doing - there are plenty of diagrams on the internet.
I assume you've checked the pump? The pipe run for the hot water circuit is often short enough that, even with a dodgy pump, the water will heat. Whereas the CH circuit needs more oompf. Our previous house was like that.
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On 19/11/2018 22:51, Brian Reay wrote:

We probably have the nicest set of diagrams out there:
http://wiki.diyfaq.org.uk/index.php/Central_Heating_Controls_and_Zoning
Downloadable version:
http://www.diyfaq.org.uk/docs/Sundial-Wiring-Rev1d-2nd%20Edition.pdf
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On Tue, 20 Nov 2018 00:16:29 -0000, John Rumm

Yes this was my first port of call before posting.
I'll check the wires to the valve when I am next there but as the boiler is due for a service I'll see what the guy doing the work thinks, in the meanwhile it's possible to run the heating by manually operating the diverter valve.
AJH
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On 19/11/2018 20:16, AJH wrote:

So what did you mean by "2 way valve"? I took that to mean 2-port valve, which simply turns flow on or off. Did you mean a valve with one input and two outputs - in other words a THREE port valve?
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wrote:

I should have said a 3 port valve with two positions, I'm not very au fait with wet stuff or the terminology and was trying to identify the system from the wiki.
AJH
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AJH formulated on Tuesday :

Probably a three port, but with three positions. CH, or HW, or HW + CH (sharing the flow).
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On 19/11/2018 18:14, AJH wrote:

The quick way to check it to look at how many wires are in the flex from the valve. Y plan ones have 5, and diversion valves only three.

On the standard Honeywell style valve, there is no microswitch or feedback. Just power on, for hot water, and power off for CH.
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On 19/11/2018 18:14, AJH wrote:

Also the HW demand must be satisfied before the CH can be heated.
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