suprima 100L HW no CH

[toothman]

ok, i've searched around for this problem and it seems quite common, but most answers relate to checking a 3 port valve, but i have 2 * 2ports. Anyway heres the problem!

Up until last week i could have CH on with HW and everthing worked fine. Now though i can only have CH when HW is on.

Boiler is Suprima 100L,
2 * 2 port valves which whirr and open/ close when cylinder or room stat turned up or down,
Pump runs ok

If i select CH only, boiler turns pump on and valve opens, but cold water just circulates and the boiler does not fire up.(i know its circulating in the system because if i heat the rads using CH & HW selected on controller, then turn off just HW and open a previously cold radiator it gets warm, but eventually the system goes cold as boiler wont fire).

I checked valve wiring, and when CH is selected and room stat turned up the following are live (Danfoss HPA2) - Orange, grey, brown all live. With room stat turned down just grey is live.

So what else can i check?

As i said before up until last week, i was able to have just CH on without HW, so the programmer and system must be plumbed & wired to allow that option. I just dont understand why its gone funny now!

Any help much appreciated, even if its just a link to another thread which i've missed!

Martin

 

[toothman]

heres a bit more info...

If i turn the CH on by itself the boiler CH 2 port valve opens and pump starts. Boiler fires up, but only burns for a couple of seconds then cuts out. No lockout though.

With HW on, the fire up sequence works fine and boiler continues to burn.

Just to confuse me more, it ran for about 15 mins this morning with just CH on before it decided to turn off, but has now gone back into its not working at all mood!

Cheers,

Martin

 

[ChrisR]

Boiler doesn't know whether its heating CH or HW, but if it brings the pump on it knows it should be on.
COuld be a blockage on the CH side - but then the boiler would come on long enough to get itself hot.
If it doesn't get really hot I'd change the temperature sensor - it may think it's hot enough (from heating the HW) But you'd expect it to come on eventually even if it had "drifted".

 

[toothman]

ok i've just swapped over the 2 port valves (and reconnected the wiring accordingly!) and at seems to be working so i can now have CH only without hot water. I tried HW only......and.......it fired then ran for about a min (cylinder not upto temp) then cut out. Basically did what the CH has been doing!

So (touching lots of wood here!) it seems to me its the zone valve. But i'll let it run for a few hours then retry the HW only, CH only scenarios and see before i get one.

If it is, where should i get one from? PLumbcenter or is there a cheap online store anyone can reccomend.

Obviously though, knowing my luck it'll pack in again in half an hour

Martin

 

[weareleeds]

Most likely cause is boiler pcb a lot of problems are encountered in field with potterton suprima pcb's. If the reset button is a little dimple it is the original board if there is a little black button to press it is a mark 2 board.the new modified one needs a total rewire of boiler & takes a pro approx 30 to 40 mins to do

 

[toothman]

well its still working!

I replaced the dodgy actuator (28 quid inc vat) and both HW + CH can be on independantly now. Hopefully it will stay that way...fingers crossed!

So even though my actuator was opening + closing the valve and whirring away, why wasnt the boiler staying lit? Is there a switch in the valve that tells the boiler it has opened fully or something? I assume this must be the case as there's 4 wires coming from it and it should only need 2 for the motor? correct?

Anyone want to give me a quick actuator lesson??

Cheers,

Martin

 

[ChrisR]

Why not try google?????????????????????

http://content.honeywell.com/uk/homes/Catalogue/Heating Controls/2.19 V4043.pdf

 

[weareleeds]

Brown wire is live to motor Blue obviously neutral orange & grey are switching (one should be permanently live) the other powers up the blr when fully open

 

[MANDATE]

My opinion is a faulty microswitch giving a intermittant problem.
I replaced a actuator on a 3 port valve, then dismantled the original. Knowing the fault was a microswitch I dismantled the microswitch to find nothing more than loose carbon on the contacts and after removal it was ok.