Thermostats again

[Budgie]

Have a new condensing CH boiler running 12 radiators, 11 with thermostats. The one without is in the hall near the main thermostat mounted on the wall, set at 23 degrees. The boiler has a separate integral water temperature control, currently set to a 70 degrees maximum.

If all radiator thermostats are opened fully, there is insufficient pressure to heat all effectively - the two in the lounge are on the end of a longish loop. The house is currently only just warm enough.

If I increase the water temperature, surely this will make no difference to the room heating, as this is controlled by radiator thermostats. If I increase the main thermostat, the same is true (but the hall would be nice and warm!) However, both options will presumably burn more expensive gas.

What's the point of the boiler control? What's the best option for maximising heat?

[visionset]

Looks like the rads need balancing.

It sets the internal thermostat for the temperature the boiler heats the CH water to. If your rads cool the water down faster than your boiler can heat it up then the thermostat won't do anything but this probably means your boiler is underpowered for your heating requirements.

1st of all balance your rads!

-- Mike W

[Cicero]

=============================== How close is the thermostat to the radiator? If it's too close it could shut the boiler down prematurely before the other radiators have had time to heat up. You could try setting this thermostat much higher (temporarily) to see if it improves the heat in the other radiators.

Cic.

[Andrew Gabriel]

I experimented with this when doing my central heating. It turns out one of the worse places is on the opposite wall from the radiator. You tend to get a warm airflow rising from the raditor, going across the ceiling, and down the opposite wall, giving a temperature reading which is significantly higher than most of the room. The best position from this point of view seems to be on one of the walls ajacent to the radiator wall, or the radiator wall itself but some distance from the radiator. Of course there are many other factors in a room which can also cause significant disturbance to meaningful temperature measuring, which you should also take into account.

[Budgie]

Sorry for the delayed reply.

Wall thermostat is 1.6m high on wall of 1.8m wide hall, opposite radiator. Both are near front (double-glazed) door.

If it does improve heat to radiators, what is the conclusion?

[Cicero]

================================ To a certain extent it depends on what size the radiator is, although I would consider that the radiator and thermostat are too close in any case unless the radiator is very small. If the temperature in other rooms improves as a result of raising the thermostat setting to a substantially higher setting then there are two possible alternatives. The first would be to turn the radiator down to a very low heat output (close down the lockshield valve almost completely) and the second would be to re-site either the radiator or the thermostat.

Consider the information in Andrew Gabriel's reply which suggests that there is an extraneous source of heat hitting the thermostat in addition to the directly transmitted heat.

If you can't get a much greater distance between thermostat and radiator or turning it down to a low output doesn't work then you may have to re-site the thermostat to another more suitable room.

All the above, of course, depends upon my suggestion (thermostat causing premature boiler shutdown) being correct. If you try my suggestion and it doesn't work then obviously there's something else causing the problem.

Cic.

[Budgie]

Thanks all, for the replies.

The replacement boiler was recently fitted by BG (yes, I know) and doesn't seem to heat the rads as quickly as the previous one - I believe it heats the water cylinder first, then sets to on the CH.

Anyway, moving the thermostat isn't a DIY option for me, so we'll see how it goes as the weather disimproves!

[The Natural Philosopher]

That's down to how your timer works, and also how hot the boiler temp is set.

[Roger Mills]

The heat given out by a radiator depends on the *difference* in temperature between the radiator (mean of water input and output) and the room. So if you increase the radiator temperature, you get more heat from it. This assumes that the boiler can keep up with the increased demand. A thermostatic valve on a radiator responds to *room* temperature, not water temperature. So if the room is below the target temperature, the TRV will be fully open, and increasing the water temperature *will* put more heat into the room.