Roomstat cutting in and out too quickly

[moss99]

Hi all , i have an issue with my continental uf system , the kitchen roomstat is a rotary dial type, i noticed the heating pump was cutting in and out quite often because this stat is cutting in and out too quickly , i swapped it for one from my office and it does the same thing .
I rigged up a thermocouple next too it and started taking note of the temps it will cut out at 23.7 ° then will cut back in sometimes less than a minute temp still at 23.7 °
.
voltage going to the stat seems stable ..
whats going on here ??

 

[Alec_t]

Make/model?

 

[moss99]

sorry i accidentally posted it before i finished it

 

[Harry Bloomfield]

whats going on here ??

Where is the stat mounted? If it is too near a radiator or source of heat, that might explain it.

If it is an old fashioned bi-metal stat, then the problem with those was too wide an hysteresis (difference between on and off temperatures). They got around that by using a resistor as an heater - stat switched on, resistor warmed up the bi-metal and helped reduce the hysteresis.

 

[moss99]

Where is the stat mounted? If it is too near a radiator or source of heat, that might explain it.

If it is an old fashioned bi-metal stat, then the problem with those was too wide an hysteresis (difference between on and off temperatures). They got around that by using a resistor as an heater - stat switched on, resistor warmed up the bi-metal and helped reduce the hysteresis.

I put the thermocouple right next to it , you can see it in the photo of the stat , the temperature did not change ..

 

[Harry Bloomfield]

What happens if you disconnect the neutral from the stat? That will isolate the resistor / heater?

If that proves to be the cause, try upping the value of the resistor which will increase the hysteresis/ bring the heating on less often, but for longer on periods.

 

[moss99]

There is something adjustable on the board ,floor limitation ??

 

[Harry Bloomfield]

https://www.manualslib.com/manual/1404909/Continental-Underfloor-Heatmax-34041.html

Which says - Differential (hysteresis) 0.2C which is very tight temperature control.

..and seems it is not user configurable. The only way to reduce the frequent firing, is some sort of delay timer, so that once it has hit temperature and clicked off, it remains off for a preset amount of time.

Those instructions make no mention of the DIL switch settings nor the 'Floor Limitation' adjustment. The DIL I would guess sets the radio ID for pairing with the receiver, the 'Floor Limitation' adjustment is anyone's guess.

The latter is set to minimum, maybe try tweaking that to see what the result is?

 

[ericmark]

Think I have found manual here as said it has the option for a sensor these are normally used to electric UFH, looking at dip switches it seems to say "thermostat as room sensor with upper limit floor on external probe" however reading the instructions it does not say on/off on dip switch drawing it shows a diagram I assume black is switch position, but could be reverse?

 

[moss99]

I was considering changing to some digital controllers , maybe i should just do that ..
It does seem to have got worse though .. its going on and off several times a minute on some occasions ..

 

[Harry Bloomfield]

Think I have found

Thanks Eric, that is much more detailed than the one I dug up...

Switch 2 suggests it sets 'static differential' or 'proportional', it might be worth trying that switch in the alternative position.

 

[moss99]

do you mean flick the dip switch 2 up ?

 

[Harry Bloomfield]

Yes, try moving it to the alternative position, just to see what difference it makes to the response of the stat.

 

[Alec_t]

The manual front page says "Floor temperature limitation (low or high with the optional sensor)". That relates to the setting of the preset pot. Presumably you don't have the optional sensor (which would be floor-mounted)?

 

[moss99]

Hi , moving that switch has made a big difference seems to be working well now ,, (no floor sensor) ..
Thanks for your help ..