faulty cylinder thermostat??

[graham1]

Hi all,
would like to know how to test whether or not a satchwell side mounted cylinder thermostat is working properly. seems quite old, in a silver box with wheel dial on outside. (has S.A and P.A printed inside??) has blue, white, yellow and earthwire connected to PCB.
Details of system: potterton flamingo 40 boiler, HW cylinder, 2 tanks in loft, motorised valve and pump next to cylinder.
I can't seem to reduce the temperature of the hot water. I currently have thermostat turned down to 40 but water still heated to 60-65 ( i hear click at this point when i turn up thermostat dial, then boiler and pump switch on as i'd expect to heat water to higher temp.) thermostat is set third of way up from bottom of cylinder.
Have seen other posts where this is also associated with problems like HW heated only with CH on too but both my CH and HW (except for being able to turn down temp) work fine together or independantly as requested at programmer and room stat .
Seems like thermostat clicking at correct temp but not telling boiler to switch off at correct temp ??
would like to check/ confirm this before buying another if possible.

Thanks in advance,

Graham.

 

[gas4you]

1 terminal will be common other 2 will be live on call for heat and other live on satisfied.

I would look at your motorised valves first.

 

[graham1]

Hi gas4you.
thanks for prompt reply...thought i posted further reply but doesn't seem to be here...
Anyway, checked cylinder stat as advised and found common, white live on satisfied, yellow on demand. guess it works ok then??
Initially thought it could be motorised valve as you pointed out so replaced like for like Sunvic actuator about a month ago.
Please excuse terminology but this is how it seems to operate;
The 'semi circle' on valve visible when head is removed is turned to 'smiley face' position when HW selected. When HW and CH selected it turns through 270 degrees clockwise (or 90 degrees anti-clockwise as i don't know which way it is turned).
As said in previous post CH works and turns off at correct temperature on room stat but HW continues to heat above that selected on cylinder stat.
Is it possible valve not closing off water to cylinder properly letting it heat up DHW further?
Valve is turnable round and round with thumb and finger.

Had a look to at PCB as i found a wiring diagram on inside of cover.
Cylinder stat demand yellow is shown connected to switch then orange on actuator. Checked continuity and this is good.
Cylinder stat satisfied white is shown connected to switch then White on actuator but I can't get continuity even after turning the thermostat dial up and down??
Is this irrelevant? switch problem??

Anyway, any further advise or pointers greatly appreciated.

Graham.

 

[stardanny]

Try this.

Let heating cool down.

When cold, switch heating only on, feel the pipe from motor valve to cylinder, do it get hot? If it do, heating water is slipping through valve to hot water, so need new valve.

If I were you, I replace the cylinder stat. It may be worn out.

 

[graham1]

Hi,
Sorry for the delay in replying. I was away from home for a week.
My boiler programmer only has 3 selections;
1) Hot water
2) Off
3) Hot water and central heating

I'm not able to try what you asked as I can't select heating only.
I have one motorised valve. Input to the valve then goes to cylinder or central heating.
I can't select heating without hot water. Is my valve sending water to the cylinder and central heating?
If so, is there no way to stop the water being heated above the temperature of the cylinder stat?
The water gets to about 65degrees even when boiler is set to it's minimum.
One more thing that confuses me;
The hot water being sent from the motorised valve to the cylinder enters near the top. It then branches from this down through a turnable valve into the bottom of the cylinder then branches again down through floor (back to boiler I'm guessing) My question is should the tunable valve connecting the input at the top of the cylinder to the output at bottom be open as it is at the moment?

Thanks,

Graham.

 

[gas4you]

Sounds like this 'turnable valve' is probaly a bypass valve. Close this fully then open about 1/2 turn.

 

[graham1]

Hi, sorry for delay in reply...am away a lot from home working.

Anyway, tried what you suggested with the bypass valve but still not heating hot water correctly. Actually went up in temp by about 5 degrees according to the click on cylinder stat.
Also found that heating wouldn't come on when requested until i turned up the cylinder stat until it clicked. actuator head then turned valve and heat came on.
Is this maybe the reason the valve was fully open to begin with as a temporary solution?
Maybe as my programmer is old and can't select heating on it's own without hot water it will always heat the hot water in the tank when central heating is on?? when HW only is selected the temperature obeys the cylinder stat???
Is it worth changing the valve itself?
Is it very difficult to do?

Thanks in advance.