Frustrating Problem with CH System

[Eeeee]

Hi All

Great site ........hope you can help with a problem I have with my CH System.

My system consists of boiler ( not combi) 3 port valve, pump, room thermostat, HW cylinder, HW thermostat and timer.....

last night I noticed my radiators had gone cold in the middle of the 'on' time period

Checked timer was on - OK

Checked room thermostat was calling for heat - OK

Checked boiler - only pilot light was on

Then the interesting thing

Checked HW thermostat - this was not calling for HW as HW was up to temp, however I adjusted the HW thermostat to make it call for HW this then fired up the boiler and sent heat to the radiators. Turning this HW thermostat back down caused the boiler to go off.

It seems that the HW thermostat is bringing the boiler on regardless of what the room thermostat is asking for and I cant understand that ?

Any ideas, explanations would be appreciated........

 

[MANDATE]

From your description I would suggest you have a problem with the 3 port valve.
When you demand CH only, the valve should move across to the CH only position (unless it is already there) and yours is either not moving beyond the mid position or if it is then electric is not passing through the micro switch to ignite the boiler.
In the mid positon the boiler is not ignited through the micro switch so HW and CH share the water.
You need to observe and listen to the valve head as you try different positions, some heads can be removed and you can look at the underside while you check it.
if the valve head does move the full amount, the problem will be the microswitch. If the valve head does not go further than mid point then the problem will be the motor in the head.
motors are about £15 The microswitches are not easy to replace. A complete new head will be about £40.
suggest you do a search on 3 port valves.
I had similar problem and took ages to fathom out exactly what was going on. (microswitch failure)

 

[2face]

i agree as above .

 

[Eeeee]

Mandate, thanks for response, I'll check the valve as you suggest. I'm beginning to understand how this thing works now ........

 

[MANDATE]

And the best of luck!. There's a lot of detail that you may not need to understand. but there are a few points worth remembering.
The CH side soon loses it heat through the radiators so does not stay satisfied for long, whereas the HW side stays satisfied much longer as the cylinder is insulated and you're not constantly using hot water.
Now you may select HW/CH shared, but as soon as HW is satisfied which usually aint long the valve automatically moves to CH only, but if that is not functioning you wont get any heating until it moves back to HW/CH shared. But it's not going to move back, unless you run off and waste some hot water or increase the cylinder stat.
The valve does not return to the HW position when the system is turned off, it stays where it is. this is because there is still power being applied to the motor. But if you switched off the power to the whole system then the valve will return to HW only position.
Best way I found was turn off all power, then set to HW only, cylinder stat set low, room stat set low. Power back on and nothing should happen.
Next set cylinder stat high, motor will not move valve but boiler will flash up.
Next put cylinder stat back to low and boiler will close down.
Next select CH only nothing will happen until the room stat is turned up. Now the motor should turn the valve in two stages, first to mid position where there will be slight delay while power from one source is transferred to another source, then it will move right across to CH only.
This blocks off water to HW side and opens up CH side fully and activates the microswitch during this stage to light the boiler.
Do let us know how you go on

 

[Eeeee]

Thanks again Mandate.....

I'll probably get stuck in tomorrow.......

Do you know where I can get my hands on a 'typical' wiring diagram for this set up, this may help on this occasion and certainly with any future problems

 

[MANDATE]

Try the honeywell web site. I'm sure I've seen it there. Yours is a 'Y' plan.
If you do a search for 3 port valves or Y plan you'll find the link somewhere.