why are my rads still hot with thermostat turned to zero?

Got a standard GCH system, one of those where the bathroom rad is always hot, for some obscure reason the plumber explained but I've since forgotten.
However, I've only just noticed that even with the room stat turned all the way down, all my rads are still somewhere between warm and very (maximum) hot. I turned the stat down about 3 hours ago, and a couple of the rads are still red hot, some are pretty warm and others are lukewarm. Didn't think much of it during the freeze, but now it's turned milder I was wondering why the rads were still pumping out heat so much.
I keep the control box set to "always on" for the water and heating, I was under the impression that it could be controlled by the room stat rather than a complicated system of on/off cycles which for various reasons, don't suit me. I have no idea what route the pipes take, but none of the rads have a thermostat on them, and I've recently had to manually valve-turn a couple off because the rooms they are in, were getting so hot.
We had the triple-valve (?) replaced a few months back along with the room stat, could either of these be causing the problem? And if so, do we have any comeback on the plumber for the (presumably) astronomical gas bill we're going to get?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Upstairs?? In the old days it was called "working on gravity". This meant that a system installed by an old school plumber the upstairs rads would get warm without the pump being turned on. But that was in my day, my day is long gone.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Everything except the boiler and room stat (and obviously half the rads) is upstairs.
I've had the stat on zero since about lunchtime and one of the downstairs rads is still red hot, the others are warmish. It seems the CH is pumping heat regardless of the temperature I'm asking for. The only way to stop it is to turn the CH "off" in the water/heating control panel in the upstairs airing cupboard.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Like I said, my day is long gone. I tried. I dunno. Somebody here will know.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Lots of snips

The boiler should only run if the system is calling for heat, so I would check if the room stat is set too high, or if it's contacts have stuck together. Also if the hot water tank is calling for heat, the boiler will come on, so check the 3 way valve is not bust and sending hot water through both circuits. Be careful, as the 3 way valve is often live in certain positions, even when not moving.
Good luck.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Thanks, I'll have to get a plumber in (again). Might be worth getting a sparkie too, to rule out anything related to the stat or the wiring.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

In case it helps anyone else, plumber came out today and identified the 3-way valve as the problem. The motorised bit was working correctly and in the correct position at all times but by turning up the water stat and demanding hot water, the valve was also sending hot water to the rads when they should have been isolated.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Perhaps you have a frost stat on the boiler ??
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.