hi- low limit stats

[CXR100]

went to a job today , heating not working , anyway fault was found as a faulty programer, but anyway, it was a solid fues system with gravity hot water and pumped heating with a indirect cylinder, the cylinder was piped up in 28mm and heating in 22, there were 2 stats on the gravity , one high limit on the hw flow set to 80oc and low limit on the hw ret set at 40 oc , cananybody tell me excactly what these do , there was also a room stat but no cylinder stat, and no motorised valves, there was an electrician on site, but he didnt know how it worked.............!!! also has anybody got a decent wiring diaram fo one of these?? thanks guys as always!!!

 

[snowhead]

Pump held off until temp = 40 or greater

Pump enabled at 80 or over regardless of any other control

 

[Chalked]

As above.
one for under heat and one for over heat.

 

[AWheating]

stats wired as above, hi to run pump when stove is getting to hot, low to mek sure pump doh run untill primary/gravity return is warmed up, this stops thermal shock inside the heat exchanger (pumping cold water into hot exchanger) which can cause bad corrosion.

 

[CXR100]

cool , so its quitet easy in a way then ist it! thats for that lads! much apreciated!