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Customer complains of Intermittent heating on Y plan with Stat satisfied.
New boiler fitted last year (no permanent live required or fitted previously) on an existing Y plan system. Existing timer was a Randall 103 (no hot water off position as its a timer not a programmer). The customer wanted a digital replacement so I fitted a digital timer (only one switch live out feeding cyl stat and room stat and no H/W off connection) so I couldn't fit a programmer without significant disruption and additional wiring which the customer didn't want. All seemed well, then a few months later he asked me to fit a digital stat Honeywell (DT90E) in place of the old mechanical stat. I think their was an additional wire connected to the stat which didn't appear to be needed on the new one, so I isolated it just in case. Is it possible that the original wiring took the heating satisfied connection as a hot water off live feed?
I have been studying wiring diagrams I don't see how this fault is occurring. If the room stat is satisfied there is no power to the white and the 3 port valve should be in the H/W only position requiring power from the cyl stat to power the pump and boiler. If there is power to the grey and white. It should close off the H/W, but once the room stat is satisfied, the power on the white would stop and the valve should spring return shouldn't it?
Any help or advice would be much appreciated.
Thanks in advance.
 
Y plan generally needs a HW off afaik. Maybe download the Honeywell app - there’s a fault finding section. Could you change it for x2 2-ports?
 
If you don't have a "HW OFF" then the valve will not motor to the CH only position, it probably will work in the HW position only (spring returned) and mid-position, HW and CH.
 

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If you don't have a "HW OFF" then the valve will not motor to the CH only position, it probably will work in the HW position only (spring returned) and mid-position, HW and CH.
Thanks for the response and diagram. I understand that without the H/W off connection the valve will only supply H/W only or mid position and will not drive to heating only. This I assume could result in H/W getting too hot but I don't understand how it is bringing the heating on when the stat is satisfied. Any suggestions?
 
Even without the HW OFF then assuming both cylstat and roomstat calling the valve will be in midposition, then if the cylstat is satisfied power is supplied to terminal7 (via cylstat satisfied terminal 2) so you now have power on both the white and the grey wire and the valve will motor to the CH position only, (the orange wire then fires the boiler).
Again assuming both stats calling initially (valve mid position) and if the roomstat is satisfied then no power on the white wire and the valve will/should spring retirn to HW only and the cylstat will fire the boiler only as required?.
 

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Even without the HW OFF then assuming both cylstat and roomstat calling the valve will be in midposition, then if the cylstat is satisfied power is supplied to terminal7 (via cylstat satisfied terminal 2) so you now have power on both the white and the grey wire and the valve will motor to the CH position only, (the orange wire then fires the boiler).
Again assuming both stats calling initially (valve mid position) and if the roomstat is satisfied then no power on the white wire and the valve will/should spring retirn to HW only and the cylstat will fire the boiler only as required?.
Thanks that what I thought but apparently intermittently it brings the heating on when the roomstat is satisfied and I can't figure out why or how if the only missing wire is the H/W off connection. I'm Baffled.
 
Thanks that what I thought but apparently intermittently it brings the heating on when the roomstat is satisfied and I can't figure out why or how if the only missing wire is the H/W off connection. I'm Baffled.
Ask them if the time it comes on, is there a demand for hot water?
 
I did read somewhere that there can be 70 to 90v present on the orange wire (as normal) when the valves last port of call is CH, this orange wire also supplies a demagnetising current to the motor via resistances and in some cases can fire the boiler with stats satisfied, I think the cure was to put a rectifier on the boier switched live, or something like that.
I think a John Ward has something on that on google.
 
I did read somewhere that there can be 70 to 90v present on the orange wire (as normal) when the valves last port of call is CH, this orange wire also supplies a demagnetising current to the motor via resistances and in some cases can fire the boiler with stats satisfied, I think the cure was to put a rectifier on the boier switched live, or something like that.
I think a John Ward has something on that on google.
Thanks John, I will check this out, but I may need to get an electrician if it needs a rectifier (as I have no idea what it is or where and how to fit it). Can there be an issue with the new style pumps that organise their own pump speed? I think I read somewhere that if they have a faulty capacitor it can cause certain issues. I will search for John Wards Post.
 
They wont be able to say as the cylinder is inaccessible in the loft but I am assuming that is the case as how else could the pump and boiler fire?
Is the timer in the loft too? 🤔 Also, just realised, you only have a timer, with both cyl stat and room stat to it, so it would be bringing the heating on with the hot water. As I said, there’s no hot water off, so doesn’t know when to shut down.

John Ward/Flameport
 
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Is the timer in the loft too? 🤔 Also, just realised, you only have a timer, with both cyl stat and room stat to it, so it would be bringing the heating on with the hot water. As I said, there’s no hot water off, so doesn’t know when to shut down.

John Ward/Flameport
Going back tomorrow and I will update the thread after the visit.
The timer is in the kitchen, there is no issue when the timer is switched off only when calling for heat, Room stat satisfied presumably cyl stat calling and heating is also on intermittently. Valve must be holding in the mid position.
No H/W off connection should only prevent it driving all the way to C/H only shouldn't it?
Valve head is brand new I thought it was a sticking microswitch initially.
 
Slight correction, the terminals on the cylstat are misdrawn in the original schematic above, to avoid any confusion, I have posted the correct one, below, but I think the descriptions of operation (with no HW OFF connection) are correct.
The only way the valve can stay in midposition if its not stuck, is both stats calling, 240V on white wire via roomstat 1&3 to drive and hold the valve in midposition and 240V to fire the boiler via cylstat C&1 and term 8 to fire the boiler
 

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(obviously) should check on site that the cylstat ter2 is wired to ter7 and that the valve grey wire is wired to ter7 also, otherwise valve will not go to CH only.
 
(obviously) should check on site that the cylstat ter2 is wired to ter7 and that the valve grey wire is wired to ter7 also, otherwise valve will not go to CH only.
Hi John, Thanks for your help. I have been back today and I want to summarise the situation.
1. Timer fitted not a programmer so there is no H/W off from the clock. There is a H/W off when the cyl stat is satisfied
2. When H/W only is required (via cyl stat calling and Room stat satisfied) motorised valve is driving to mid position, when it should stay closed on the spring.
3. White wire is live 240v. When disconnected from wiring centre live feed is coming from the valve end not the stat or wiring centre.
4. This is a brand new valve top fitted to try and cure this issue initially. Possible faulty head, but what a coincidence if it is.
5. Temp solution - turn off all the rad valves when no heating is required.
Your thoughts are appreciated.
 
Very strange, with both wires still disconnected to term5 suggest disconnecting 2 wires at term7 and see if valve still goes to mid position?

Are you sure its a midposition replacement top and not a diverter valve top.

If you have still got the old head you can do a few bench tests with it?.
 
Very strange, with both wires still disconnected to term5 suggest disconnecting 2 wires at term7 and see if valve still goes to mid position?

Are you sure its a midposition replacement top and not a diverter valve top.
It says mid position on it so I assume it is. I plan to revisit next week and do the following checking for the correct voltages at each step. Room stat turned down for tests A-C
A. disconnect and leave disconnected the wire from Cyl stat to No.8 and check nothing works. (no rogue voltages apparent)
B. as above but turn the cylinder stat satisfied and check 240 on grey only
C. as above but turn cylinder stat back up and provide an external 240 supply to No8 and check 240 only on Orange (no rogue voltages apparent).
D. wire in an different new valve head and check it has the correct voltages when the stats are turned up and down

If all this fails I (or an electrician) will be rewiring the whole system.

I will update you when I have done these tests.
 
Unfortunately not.
I have traced the issue to the new valve head being faulty. Which manifested the exact same fault as the original faulty valve head, This is why it was tricky to diagnose, (that's what you get for trying to save your customer money and buying a cheaper version from Amazon!). The orange wire which is live when only hot water is required (as it is connected to the pump and boiler which are getting the feed from the cylinder stat) is back-feeding up the white wire and driving the valve to the mid position when it should be in the H/W position. It shouldn't be able to do if the diode inside is working.
Anyway my £38.34 will be returned to me from the seller within 5-7 days of them receiving the faulty part.
Thanks to all who helped, you are much appreciated.
 

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