Central Heating doesn't work unless hot water stat cold

[IanBell]

Hi there. I hope someone here can help.

My parents have an oil fired boiler controlled by a Hostmann H27XL programmer a Sunvic SA2452 cylinder stat and a Honeywell V4073A 3 port valve. There is no room stat - all the rads have thermostatic vales. Recently the pump was replaced and, possibly coincidently, things no longer work as they should. Basically the pump and boiler only fire when the cylinder stat is calling for heat. As soon as the stat reaches temperature the HW and CH both go off. Previously it was possible for the CH to work regardless of whether HW was calling for heat or not.

I have had a look at the wiring and it all looks correct and connectivity looks correct (bearing in mind absence of room stat)

I do not fully understand the motorised valve function - I understand it open either or both HW & CH circuits but does it also turn pump & boier on? If so is it likely this has failed?

Many thanks in advance

 

[ianmcd]

yes the three port vave controls everything , from the little info you have given I am guessing that the pump was changed in error when in fact it is the synchron motor in the three port valve that is faulty there should be an indicator on the valve does it move depending on what function you have selected ?

 

[IanBell]

Hi Ian

Thanks for reply. When I isolate the entire power supply the valve returns to a passive state (sounds like it's clockwork unwinding). As soon as I turn the power back on the valve appears to move to a mid point if cylinder stat is calling for heat but therafter doesn't move at all

 

[ianmcd]

OK sounds like the synchron motor is ok and you have a problem with your heating controls calling for heat, you will need a multi-meter and some electrical knowledge to test this , it is well documented how to on here in the FAQs

 

[matt1e]

Hi Ian
The three port only controls the boiler/pump when it is in the heating only position (it technically speaking doesn't even control it then) and if the synchron was gone the heating wouldn't work at all

more likely the output microswitch isn't making due to it being faulty or the valve itself isnt opening enough to let it make

there could be other reasons though, do you have a multimeter?

Matt

 

[Whitespirit66]

Why was the pump changed? Did fitting the new pump change anything?

Sounds like it could poss be microswitch in mid pos valve.

 

[IanBell]

Hi Matt

Many thanks for reply

Yes, I have a multimeter and, as far as I can tell the programmer is delivering power to the correct pins at the correct time. and the cylinder stat appears to be switching between calling for heat and SAT correctly. My understanding stops when it comes to the valve though. What should I be looking for with the valve connections? Multimeter is capable of voltage reporting as well as conectivity testing

 

[IanBell]

Hi WhiteSpirit66

Thanks for reply

Parents uncertain why pump was replaced other than it looked green and old The motorised valve and pump are in close proximity and there is slight evidence of corrosion on the valve cover where the slider lever protrudes.

 

[Whitespirit66]

Hi

Put heating only on, and see if you get 240V from the valve's orange wire. This will see if the microswich is working.

 

[matt1e]

Hi Matt

Many thanks for reply

Yes, I have a multimeter and, as far as I can tell the programmer is delivering power to the correct pins at the correct time. and the cylinder stat appears to be switching between calling for heat and SAT correctly. My understanding stops when it comes to the valve though. What should I be looking for with the valve connections? Multimeter is capable of voltage reporting as well as conectivity testing

turn on heating only and turn the room stat up
at the valves wiring terminals check that there is
230vac between
blue and grey
blue and white
blue and orange
if there is nothing on the orange then the internal microswitch isn't making

matt

 

[SimonH2]

The operation of these valves is ingenious, but not intuitive. This page explains how it works if you want to understand it.

 

[IanBell]

Hi Whitespirit66

Thanks for your help

No - nothing from orange wire when only CH on.

 

[IanBell]

Blue-Grey = 240v
Blue-White = 240v
Blue-Orange = nil

 

[matt1e]

Blue-Grey = 240v
Blue-White = 240v
Blue-Orange = nil

= valve or actuator faulty

take the actuator off the valve body if you are confident and do the test again with it separated from the valve
if you still get no power on the orange then you need a new actuator
if you now get power on the orange then the valve may be sticking or you may get away with "adjusting" the micro-switch

Matt

 

[Whitespirit66]

Sounds like either m/s not working, or contact not being made. Looks like time to fit a new actuator to your valve.