Drayton LP722 doing odd things with HW - Plea for help from Wiring guru

27 Jun 2011
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United Kingdom

I wonder if some central heating wiring expert would be good enough to give me a helping hand.

I had the following:

Greenstar 24i system boiler
Grasslin QE2 controller – set to Fully pumped)
Fully pumped system with 2 x zone valves (one for CH and one for HW)
Room stat
HW tank stat

The Motorised valves seem to function normally. The room and cylinder stats both seem to work normally with testing.

Programmer set to on 2x per day for both CH & HW as follows

HW on 5am-7am
CH on 6am-9:30am
HW on 3pm-6pm
CH on 5pm-10pm

The QE2 was fine for 5 years and all was well and working as expected. It then decided to start locking up, particularly after a powercut – talked to grasslin and they told me it was most likely the battery backup had given up the ghost of a faulty unit (5+ years old). Before the QE2 going mad all was well. HW and CH were both fully independently working and life was good.

Decided to replace the QE2 with a Drayton LP722 which is equivalent and should be a direct wire replacement (both N L 1 2 3 4). All programmed up fine (including the mid program phantom 12:00-12:00 on/off as I only need 2x on/off) and the jumper set at back for Fully pumped. I thought it was working fine but an odd thing is happening with the HW

1. IF the HW is on and in demand and the CH is off on the controller then HW is delivered to tank and CH is not (as expected).

2. IF the HW is on and in demand and the CH is on and in demand then HW is delivered to tank and CH to rads (as expected)

3. If the HW is on and in demand and the CH is on but “satisfied” (thermostat set low) then the HW refuses to work when going into demand or going into satisfiled.

As soon as I then turn the CH to off and back to on (even if it is still satisfied) then the HW works normally again (ie when satisfied it turns the motorised valve off and when in demand it turns the valve on).

It is like cycling the heating to off and then on seems to kick the HW normal operation back into life as long as the HW is on. I can then turn the hot water to off using the programmer, turn it back to on and we are back to the call for HW being ignored again if the cylinder stat calls for HW.

I don’t understand why it was all okay with the QE2 but with the LP722.

To get around this I can set the on/off times for the HW not to overlap or fall within the CH on/off times but I am keen not to have to do that.

Any thoughts ??


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> 3. If the HW is on and in demand and the CH is on but “satisfied” (thermostat set low) then the HW refuses to work when going into demand or going into satisfied.

At this stage, we need to measure the signal live from LP722's 3, to cylinder stat's input, then stat's output, finally to the HW valve's brown wire (if it is a Honeywell valve or Drayton valve), the orange wire is the switched live for boiler demand.

1st stage complete. If this throws no light then I'll measure HW valve and cyl stat.

I have done some more permutations and noticed the following:

If the heating is on first (regardless of demand or not from heating) then the HW does not work.

Took the faceplate off wall to measure voltages while programmer operational.
Note that wires 1 & 2 are not present (normal I expect)

Voltages between N 3 / 4 are as follows: 3 4
(note tank is approx 45C at time)
CH on 1st then HW on 2nd (regardless of demand) using programmer override
HW on - No demand (tank stat at Min) 67V 236V
HW on - demand (tank stat at Max) 0V 236V
Tank not being heated.........................
MV not actuating regardless of stat position
I assume the 67V is because the tank stat is open and there is some leakage somewhere (maybe indicates deeper / different issue)?!?

So long as I put the HW on first then it all works as expected and the voltages are normal...

HW on and heating off using programmer override
Voltages between N + 3 / 4 are now as follows: 3 4
HW No demand 236V 27V
HW with demand 236V 27V
Tank being heated when demand
Motorised Valve operating normally when going from demand / no demand / demand

HW on 1st and CH on 2nd (regardless of demand) using programmer override
Voltages between n + 3 /4 are now as follows 3 4
HW no demand 236V 236V
HW demand 236V 236V

Most strange. but hopefully some wise person will have seen this exact scenario before and will be able to say why it is doing this. I am assuming that the QE2 was operating normally (before it packed in) but it might have just been that the HW always came on before the CH
... just to add to that. Then long and short of it is that my HW always starts before the heating so 99% of the time its not an issue. I tried to boost the HW that had turned off while the CH was still on and it didn't work. That's how I found out. I rarely do this.

I guess If I need to then I could adv the CH or set it to "OFF" (to turn it off) then boost the HW and then adv the CH to turn it back on or put it back to "TIMED". That seems to cover the need to boost the HW while the CH is still on and it works as it follows the logic of HW on followed by CH.

I would like to know what wiring is screwed up though - prefer it to be right so I don't have to explain all that to the other half when she wants to boost the water for a bath :(

I also took a peek at the wiring centre below the controller. It is not a nice numbered job with 1-16. It is a mass of wires inside a raised double pattress using 3 or 4 lots of terminal blocks with no numbers - nice!! I could work it all out eventually but it will take a good day I suspect and I don't want to damage boiler.

The QE2 was not mine (inherited from previous owners) but looks aftermarket. Could it be that this was wired wrong when it was used to replace the original controller (no idea what). Perhaps it was a single channel??? But even if that were the case then I can't see how as surely they would have just seperated teh CH on and the HW on wires (there are only 4 wires after all and two of them are N and Perm. Live. that only leaves 2 wires and surely they must go to the 3 & 4 positions. Unless - they went into the spaghetti junction and titted about.
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Post a picture of the wiring centre (with cover removed) along with room and cyl stat (cover removed), also a picture of programmer back plate.
How did you mange to check voltage @ programmer backplate with programmer facia removed?.. Terminals 1 2 3 & 4 'SHOULD' have no voltage.
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a picture paints a thousand words...
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Gotta be a faulty programmer, I cant see how a wiring fault would give these readings

I did the testing with the plate off the wall but the controller properly attached. You can then do the testing with a multimeter at the rear of the backplate.

I've done a bit more troubleshooting and removed 3&4 wires so only L & N are connected. I then did various on and off's for the heating and water and the relays don't seem to be triggering consistently on the programmer. The light comes on when its meant to but sometimes the relay triggers and sometimes it doesn't. This leads me to think that the programmer is the heart of the issue as the relays should trigger with only L & N attached (thus removing the rest of the wiring from the equasion??? Is this a true statement??? Could that induced 67V and 27V be blowing the programmers???

I did a reset of the unit SET & + for 5 + seconds and once I did this the relays started to behave in a different manner but still not consistent. I then took the unit apart and (without power) did a reset and also shorted the +/- of the inbuilt battery (to try and "cold" reset it).

Still no joy - the shorting of the built-in battery did not seem to have the desired effect as the time was still preserved when I put it all back together and turned it on. I think the unit is foobar. Sadly it was cheap 2nd hand off ebay (but assured it was taken from a working system during an upgrade).

What I still am not 100% sure of is whether the wiring could somehow be knackering the units (bearing in mind the QE2 went south prior) or whether I've just been unlucky and replaced one bad unit with a second different make that is also faulty. I guess the only way to know for sure is to get a 3rd unit (I guess brand new) and see if that works.

Gotta be a faulty programmer, I cant see how a wiring fault would give these readings
I'm thinking that too.

Can I be that unlucky though.....
Any recommendations on a reliable programmer. I only need separate independant control of the HW and CH, same times every day but CH and HW on for differing lengths.
Prefer mechanical with no relays if available but I can only see timers that either have relays or timers that are mechanical but the HW and CH must be controlled together for the same periods

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Remove programmer from back plate and test the operation of controls by removing cores from 3 & 4 and using 'L' to test.
Post a picture of the wiring centre (with cover removed) along with room and cyl stat (cover removed), also a picture of programmer back plate.
photos here would be a great help,maybe several of the terminal strips in the wiring centre.

There could be a wiring defect but after reading the replacement programmer is a secondhand ebay item (untested) could also be defective.
I've previously had a fault with a programmer whereby either one relay would operate normally when timed to come on, but when two relays were energised the unit would behave erratically. I put this down to the programmer's PSU failing and left it at that. Replacement of the programmer made the problem go away.

I respectfully suggest that you buy a new programmer, cost is about £50 or, if you'rs tempted to go the secondhand route again, instead of having to spend a whole day checking out the wiring fruitlessly get a paper round for a few weeks, or do a couple of nightshifts at Tesco to earn the money for a new one....

Hope this helps, well at least the first paragraph may.

thanks all.
I will get a new "brand new" controller as a 1st step and see if all is well. If not then I will resurrect the thread.
however.... before I do that does anyone have a view as to the most reliable. When I trawl amazon and the forums I see that there are loads of complaints about most of the makes - especially the Drayton Lifestyle's and relays failing and doing random things (like mine) and also the Honeywell ST9400C gets very polarised reviews - many 5* but also many people moaning about some "Bad Batch" that has been doing the rounds since 2012 - again due to relays not firing or going bezerk and not following the logic.

It seems from my research that some of these are rather fragile beasts.


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