SYMPTOM - H/W but no CH

[deagle]

Hi,

Boiler fires ok in h/w mode but refuses to fire in CH mode.

Thermostat looks ok - clicks when powered and moved above ambient temp. Also overriding thermostat (shorting the live to call) does not cause CH to fire.

I think that I have a faulty mid-position valve (ACL 679H340-30L0)

It is always set in the W position. Checking the live voltages offered by the wiring centre to the valve, I get....

---------------ORANGE GREY WHITE
ALL OFF -------> NO YES NO
H/W ONLY-----> YES NO YES
CH ONLY -----> NO YES YES
BOTH -------> YES NO YES

But... the last one puzzles me - why would BOTH be the same as H/W only.

Any ideas ?

Thanks

Deag

 

[deagle]

Oh, I forgot to add.....

If I set the Mid position valve to locked using the manual lever - which is both outlet ports open - then I can get hot water to the radiators (as expected) ....but only if the h/w is on (not if c/h is on only).

 

[matt1e]

hi
in HW only you should not have power to the white, in saying that, in CH only you do have power on grey and white so you have to have power on orange so yes suspect the valve

matt

 

[seco services]

faulty motor not powering over valve to heating heating/hw.


---------------ORANGE GREY WHITE
ALL OFF -------> NO YES NO - ok
H/W ONLY-----> YES NO YES - wrong
CH ONLY -----> NO YES YES - should be live on orange
BOTH -------> YES NO YES - yes, orange will only be live cause it
in the same terminal as the hw stat live

 

[D_Hailsham]

If I set the Mid position valve to locked using the manual lever - which is both outlet ports open - then I can get hot water to the radiators (as expected) ....but only if the h/w is on (not if c/h is on only).

That's to be expected. In HW only and mid-position (HW plus CH) the boiler is supplied through the HW thermostat. So, if you lock the valve in mid position, and the HW is off - at either the cylinder stat or the timer - then the boiler will not light.

Turn the power off to the system completely (just setting the timer to CH OFF and HW OFF is not sufficient) so the mid position valve resets to the HW port open position.

Set HW and CH timers to OFF
Turn HW and CH stats to minimum
Turn electricity on
Turn HW ON at timer and HW stat to MAX - the boiler should light.
Check voltages on valve white and grey wires - should both be zero.
Turn CH on at timer and set CH stat to max - boiler should continue to run and rads get hot.
Check voltage on White (should be 240v) and Grey (should be 0v).
Turn HW stat to MIN - boiler should continue to run.
Check voltage on White (240v) and Grey (240v)
Turn HW OFF at timer - boiler should continue to run.
Check voltage on White (240v) and Grey (240v).

Report findings.

 

[matt1e]

Turn HW stat to MIN - boiler should continue to run.

just a quick point Deagal it is normal for the boiler to shut down then fire up again after a few seconds at this stage

 

[steved101]

another faulty motorised valve problem!! as above, the motor is not moving acorss. fit a new motor or actuator head.

saying that, as well as using a multimeter, if when htg is ON, the manual leer has resistance, then this too will prove that the motor has failed to open the valve fully to the CH circuit.

 

[D_Hailsham]

Turn HW stat to MIN - boiler should continue to run.

just a quick point Deagal it is normal for the boiler to shut down then fire up again after a few seconds at this stage

Thanks for mentioning that - I overlooked the slight delay while the valve moves from mid pos to CH only and boiler control changes from HW stat to the orange wire.

 

[deagle]

If I set the Mid position valve to locked using the manual lever - which is both outlet ports open - then I can get hot water to the radiators (as expected) ....but only if the h/w is on (not if c/h is on only).

That's to be expected. In HW only and mid-position (HW plus CH) the boiler is supplied through the HW thermostat. So, if you lock the valve in mid position, and the HW is off - at either the cylinder stat or the timer - then the boiler will not light.

Turn the power off to the system completely (just setting the timer to CH OFF and HW OFF is not sufficient) so the mid position valve resets to the HW port open position.

Set HW and CH timers to OFF ( DONE)
Turn HW and CH stats to minimum (DONE)
Turn electricity on (DONE)
Turn HW ON at timer and HW stat to MAX - the boiler should light. (YES)
Check voltages on valve white and grey wires - should both be zero. (NO....GREY ZERO BUT WHITE LIVE, VALVE IN W POSITION)
Turn CH on at timer and set CH stat to max - boiler should continue to run and rads get hot. (NO....VALVE STILL IN W POSITION - NO FLOW TO RADS)
Check voltage on White (should be 240v) and Grey (should be 0v). (NO....WHITE LIVE, GREY ZERO)
Turn HW stat to MIN - boiler should continue to run. (NO...STOPPED)
Check voltage on White (240v) and Grey (240v) (NO... WHITE ZERO, GREY LIVE)
Turn HW OFF at timer - boiler should continue to run. (NO....STOPPED)
Check voltage on White (240v) and Grey (240v). (YES BOTH LIVE).

Report findings.

As requested, I have rechecked and my replies in CAPITALS above. I have also confirmed my original results and can confirm the readings. In each case I am measuring the voltage between the BLUE (Neutral) and the wire in question at the LWC1 wiring centre.

In the meantime, I have locked the manual lever on the midpoint valve... for reasons of warmth

Could I have a screwy programmer ?

 

[jobloggs]

Hi Deagle.

When on h/w only what voltage have you got on white? I seem to have the same problem as you have with the live readings the same as you report with the exception that on H/W only the white is 140 volts. All other live readings are 230 volts as expected.

 

[deagle]

Thanks for the replies folks...

Joebloggs... I will check tomorrow. Have had a glass of wine now (festive spirit etc) - I am old and wise enough to know that alcohol & electrics don't mix

Oh, and I am not sure if this is relevant but British gas fitted a new fan and APS tube to the boiler last Friday. But all seemed well over the weekend.

I appreciate the help.


Can the failure of the Synchron motor cause the voltage readings to change ? It seems to have some interesting properties as described here.

http://www.gasheating.co.uk/Mid-Position-Valve.html

 

[samparker]

why all the fuss!!

if your white wire is live when hw only is on, then the programmer is sending false signals - and is faulty!!!

 

[matt1e]

why all the fuss!!

if your white wire is live when hw only is on, then the programmer is sending false signals - and is faulty!!!

although it could be
this can also happen if the micro switch is stuck in its H position

if you have a multimeter deagle and are competent
take out the white grey and orange out of the wiring centre and check readings

HW and CH off white connection 0
grey connection 230
orange connection 0

now HW on cyl stat up white 0
grey 0
orange 230 (the boiler should also fire)

now turn the cyl stat down white 0
grey 230
orange 0 (boiler will shut down

now turn on CH and room stat up white 230
grey 230
orange 0
if you want to check the function off the room stat turn it down and white should go to 0
if readings as above all wiring correct change/repair the valve

please note readings on colours above refer to where they connect not the actual colours themselves

matt

 

[samparker]

if the 3 port mid position valve was stuck in the HTG only position, then the heating would be on all the time though.... or you'd not get any hot water.

as you say the valve could be stuck in the heating position; but there has to be an easier way of checking for that?!!! if ou remove all of the wires from the wiring centre, then when you do the test you wrote, the reading won't show up!!

basically, if your htg is on (white wire live) when only hw is on... to test...
turn power off to spur. remove the wire from the programmer that goes to the white wire from the 3 port, in the terminal box .

turn power on again and test. if when hw only is on, heating does not come on, then you know the programmer is faulty. if it still does, then the 3 port's microswitch is stuck!!

 

[deagle]

I definitely don't get heating on all the time. Indeed the only way that I can get heating is by locking the valve in the mid position and firing up the hot water.

My curent plan of action :-
1. Remove and inspect the motor and microswitches as per Neale's post here....

http://pub47.bravenet.com/forum/4002063021/show/806800

2. If that fails, I am tempted to replace the mid position valve (now obsolete) with a MA1/679-3 which claims to be electrically and physically the same. Of course, this will require part draining the system to below the valve which is in the airing cupboard up stairs - is there any easy way of telling when it is low enough ?

I had fernox added last time work was done on the wet side of it and I don't really want to wash it all down the drain. I guess I could collect it in a bucket or two and refill back from the header tank ?

Of course none of this will help if the programmer is faulty !