CH only works if HW already on, after replacing 3-port valve

[matt1e]

You seemed to be saying that you had to have HW OFF connected to grey or you would never get CH only.

You wouldn't......well not by walking up to the programmer and selecting CH only anyway, which is what I meant by on its own (and what i think the op means)

i.e central heating without hotwater
He could of course turn the cylinder stat right down but he would still have to select both hot water and central heating at the programmer for it to work


Matt

 

[warney]

hi chris
it probable it has been a bodge from the start and you always had to have hot water on with central heating
difference now is the plumber who changed the valve has bodged it up even more and has wired it so the boiler is getting "backfed" via the pump live connection and detecting this as a pump wiring fault and going into lockout (he's probably connected the pump, the roomstat return, and the boiler pump connection together)
its hard to see from your photos where the pump core colours are connected can you elaborate? the pump live should be connected to one cable only and that will be none of the valve connections
also where do the two flexs going to the boiler connect to?another connection box? as they must join on to the threecore mains cables coming into the wiring centre somehow

Matt

I'll check this in due course (prob not for a day or two, though). Although I think everything goes to the single box in the airing cupboard. There are the three cables for the valve,pump and tank stat, plus three cables coming out of the wall, one of which is the room stat, and the other two presumably are the boiler and mains. The pump "live" is, I think, connected to the orange valve cable and a red cable to the stat.

It's the lockout which is causing me the most concern. I guess if I could "re-bodge" it so that when CH only is selected it actually services both CH and HW circuits, that would do, as long as when HW only was selected it was actually HW only :

e.g.

Selected Actual
HW ----> HW
CH ----> HW & CH
HW & CH ----> HW & CH

I don't see that would be a problem. I assume it wouldn't cause any safety concerns - it would just mean when the CH was on, the HW would be heated to a temperature close to that of the boiler output, rather than what's dictated by the tank thermostat.

 

[matt1e]

The pump "live" is, I think, connected to the orange valve cable and a red cable to the stat.

The orange should not be connected to the pump at all your "wiring centre"has been trashed by the plumber who fitted the new valve to it! can you not get him back out?

matt

 

[matt1e]

sorry just reread your first post you cant track him down!!!
do you possess a multimeter?
if not and bearing in mind you dont have a cable connected to the programmer hot water off terminal

please follow instructions and answer the following

turn the roomstat down
turn the cylynder stat up
turn off HW and CH at the programmer and at the boiler spur
check that the mid position valve is at its rest (hot Water)position
now

1) turn on the spur and select hot water only

does the boiler fire and does the valve stay where it is?

2)while you are there checking the valve position turn down the cylinder stat

does the boiler go out and does the valve stay where it is?

if the answer is yes to both then so far so good

3)now turn the cylinder stat back up to fire the boiler again and select CH on at the programmer (leave the HW switched on and the room stat down)

is boiler the boiler still firing and is the valve still in the hot water position?

if the valve moves in steps 1,2 or 3 please state which step and which position it moves to

Matt

 

[warney]

do you possess a multimeter?

Matt

Yep - I've got a multimeter (and a mains tester screwdriver!).

Chris

 

[warney]

OK, I've followed your instructions!

turn the roomstat down
turn the cylynder stat up
turn off HW and CH at the programmer and at the boiler spur
check that the mid position valve is at its rest (hot Water)position
now

Yep - valve at HW (top) position

1) turn on the spur and select hot water only

does the boiler fire and does the valve stay where it is?
Yes

2)while you are there checking the valve position turn down the cylinder stat
does the boiler go out and does the valve stay where it is?
Couldn't test this as water didn't come up to temp whilst I was there

3)now turn the cylinder stat back up to fire the boiler again and select CH on at the programmer (leave the HW switched on and the room stat down)

is boiler the boiler still firing and is the valve still in the hot water position?

Yes to both

Additionally, when turning the room stat up, the valve moves to the mid position (as it should, I guess).

One other thing I noticed, after turning CH and HW off at the boiler, the pump continued to run for a couple of minutes before stopping.

Matt

As regards the actual wiring, the pump is definitely connected to the orange valve wire. The junction box in the airing cupboard has nine connecting blocks, as per the photos I posted before.
As far as I can make out, the connections to each one is as follows :

1) Common earth

2) Red from room stat, yellow (middle cable)

3) White from 3-port valve, yellow from room stat

4) Common Neutral (Blue wires)

5) Orange from valve, Brown from Pump, Red (Top cable)

6) Earth, Yellow (Top cable)

7) Blue (top cable), Black from tank stat

8 ) Brown from tank stat, Red (middle cable)

9) Grey from Valve, Black from tank stat

The "top" and "middle" cables go into the wall, and I'm not sure to what they connect. One must go to the boiler, but perhaps they both do?
The top cable has Yellow, Red and Blue wires, the middle cable has Red, Yellow and Earth wires.

 

[matt1e]

Hi chris regarding your first post, is the middle cable definately the pump and not the cylinder stat? as there is definately at least one black core connected from this cable

middle white cable pump and bottom cable HW stat. The second pic shows the connections to the rest of the house (boiler,roomstat etc). Nothing's labelled which is why I'm having such a problem working it out!

Junction Box

• warney
• 12 Dec 2009
• 1

if your last post is correct then

5) Orange from valve, Brown from Pump, Red (Top cable)

disconnect the orange from here and put it in a connector or insulate it for now

now turn on HW and while the boiler is firing with your multimeter measure between

4 (neutral) and 7 (230V ish??)
then
4 and 8 (230V ish??)
then
4 and 9 (0V ish)

if you get the above readings then manually turn the cylinder stat right down (there will either be a knob on the front or a slot for a screwdriver) if the boiler doesnt shut down straight away wait till it does and repeat the above tests
4 and 9 should now be reading 230 and either 4and 7 or 4 and 8 should be reading 0v (probs 4 and 7)
whichever one is now 0V is where you now connect the orange to
because of the lack of the HW off connection at the programmer this will not give you the option to select heating on its own (well you can but the boiler wont fire)but it will allow the system to toggle over to heating only when both are on and the hot water gets to temp and should stop the lockout

One other thing I noticed, after turning CH and HW off at the boiler, the pump continued to run for a couple of minutes before stopping.

Thats pump over run and normal
Matt

 

[warney]

Matt, you're an absolute star!

I attacked the airing cupbaord with my multimeter and it was exactly as you described. I then swapped over the orange wire, and now it all works perfectly!

Strangely, I can even get CH only without HW. I realised the tank stat goes into a separate control unit on which you set the temperature ( Potterton PTT2) , so perhaps this then sends a "no HW" signal?

Anyway, as I say it all apperas to work perfectly now, so I guess the plumber simply wired in the new valve incorrectly.

Again, many many thanks to Matt and everyone else who helped with this - it's saved me a heap load of trouble (and cash!).