Turning radiator off/down - no thermostat valve

Nothing to put a spanner on! Thermostatic Radiator Valves (TVRs) have a spring loaded pin that is pushed down by the TRV head with the amount of travel being controlled by temperature. The head of a TVR can be removed by unscrewing it leaving the valve with the pin - in the fully open position. The screw on cap ensures that the pin is fully down and the valve fully closed.

If you want to remove a radiator you either drain down the whole system or just close the valves on BOTH sides of a radiator and drain just the water in the radiator. The decorators cap for the TRV on one side of a radiator ensures that that valve stays shut. If the head of the TRV was just screwed down to close the valve the valve may open again as the temperature drops. In normal operation you probably would want a TRV to be open (or partially open) for frost protection at 5 to 10C.

With a TRV the latter for automatically turning off the radiator at a user selected temperature.

In a room with a room thermostat it's better to have two lockshield valves which cannot be adjusted without a spanner and with a cosmetic covering caps to discourage tampering and let the thermostat control the temperature by firing up or turning off the boiler.

Ah yes gotcha!

They replace the thermostatic valve when decorating, not permanently.

TRVs only have a pressure operated plunger, you can't set their position with a spanner. Normally the wax cartridge in the TRV head modulates the amount of plunge. With the TRV head removed the plunger is in its fully open "unplunged" state. So you need a way of pushing it down.

(taking off the TRV head and inserting a 5p coin before replacing it will also work)

If your house had effective insulation, that move would not have made much, if any difference.

At the time very large single glazed windows - now double glazed and much heavier curtains. I tend to keep most of the house cool(ish) in winter by having TVRs turned down and have only my living room at a higher heating level. I prefer a cold bedroom.

I understand that, and as stated at the start of my OP, the bathroom radiator has no thermostat. It surely doesn't need another radiator in an adjacent space to also provide a bypass.

I'm pretty sure I've mentioned there are no room thermostats.

I probably don't - term confusion and ignorance. The little caps to that fit on top of the unsightly brass spindle and then get knocked off when SWMBO goes round with the "sucker" device that swallows up any loose item, useful or not.

Now I have to have all internal doors open or the cat kicks off.

But if you are allowed to shut doors the movable thermostat would work.

BTW cavity wall insulation knocked 30% off my heating bills - non standard construction with a gable end facing Emley Moor

Has the bathroom rad got a manual valve on it? If so that would be one reason an installer would leave another path open since a end user could shut off the bathroom rad.

Apart from SWMBO who, if typical, will always be calling for heat

That's your no 1 problem to solve then. Systems with no room stat are quite wasteful.

Thanks. I thought that was always likely but wanted to just check.

As for terminology, I've seen them called various things - from memory "safety caps", "valve cap", and "valve cover". "Decorator's cap" would be a logical addition given it's not a good idea to get paint on the valves.

Both rads are identical with identical connections, though the one in the hall is twice the size. Neither have any manual adjustment ie they both need a spanner to alter settings.

I'm struggling to understand the logic of the problem. If the hall radiator had a manual valve I'd turn it down to off. How does the system know the difference between doing that and turning the lockshield (is that the right terminolgy) off? Presumably I'm just going to raise the temperature of all the other rads on the system causing their TRVs to kick in and thus for the boiller temperature control to limit the boiler and reduce my gas consumption.

I can understand the scenario where the boiler is controlled solely by a thermostat in a room and if that was the room where I'd turned off the radiator the boiler would think it was always cold but that isn't my situation. I have the temperature control on the boiler set to 1 or 2 in cooler weather and wind it up to about 5 or 6 when it is really cold, and adjust the timer for day/night and additionally for if we are in/out. All very 1960s but no second guessing required.

I keep procrastinating about changing the boiler (combi) - it is 16yrs old. Now I don't know what to do for the long (next 10-15yrs) term.

Tell me about it. Not helped by SWMBO originating from a tropical area. She would have the heating on now that the summer heat has gone.

It may be worth considering your options now as in the next few years the installation of new gas boilers may be discouraged in favour of air sourced heat pumps or all electric heating. With a update consider some of the more modern forms of room thermostats or temperature control.

It does not know the difference - either will cut off flow through the rad. The purpose of the single lockshield valve on rads with manual or TRV controls is to set the maximum flow through the rad. This allows the system to be balanced.

TRVs do not respond directly to the temperature of the flow through the rad or even its temperature directly. They are supposed to respond just to the room temperature.

So diverting more flow through a rad may pass heat to that room faster, and cause the TRV to close sooner that it otherwise might.

If you reach the stage where the return temperature of the water to the boiler exceeds its internal thermostat's set point, then the boiler will cease firing. However it is still in a "call for heat" mode, and will be running its pump, and waiting for the temperature to fall. At which point it will fire again. Hence it will continuously be using energy (electric pump etc), and periodically firing for short periods just trying to sense what the actual demand for heat from the house is. Heat that much of the time the house may not need.

This is a very inefficient way of running a heating system.

ISTM that is exactly your situation. You in effect have the thermostat "call for heat" input to the boiler hardwire to "on" permanently. So your only controls on it are a timer, and its internal stat.

That means any time the heating is on, it will spend a period of time "idling" while it waits for the house to need heat again.

Proper controls will ensure that does not happen, and save fairly significant amount of energy, while also possibly improving comfort in the house since you don't get so many temperature overshoots in the bypass paths when the boiler fires for a few mins, gets the system water up to temp, and then shuts off again.

In effect you are running manual weather compensation, which is fine. With updated controls you could have the system do that for you (and with finer grained control) if you wanted.

What are the options? Is the house well enough insulated that it could work with a lower temperature heat source? If the answer is no, and you are not planning on increasing the insulation to that level, then you are looking at another boiler of some sort.

A new boiler will also *require*[1] updated controls since what you currently have does not meet building regs and an installer would not be able to sign off the install.