thermostats

Twizz

Hi, TRV controls the room temp of each room and the wall stat controls the boiller.wall stat is best put in the hall-way and the rad that is in the hall-way has NO trv (remove it if it has one) now the wall stat is the boilers on off switch and this is controled by the rad in the hall, set to 20c when the hall is up to temp the boiler will turn off. set trv's to 3 or the mark that is on them then you may have to play with them to get your desirable room temp.

The best place for your trv.s is on the flow side of rads, then you reduce the return valve so you get max temp out of your rad (ie close valve and reopen one full turn) The intention is to even out the flow of water through each radiator so that with the system in its normal operating condition, the temperature drop across each radiator is about 20°F (12°C).

Magentasue

The set-up described by twizz is what we have and it's working well.

Cardew

Premier wrote: »

Yes, its a safety device built into the boiler to prevent damage when the return temperature is too high.

But just like in a car with a rev limiter which shouldn't be relied upon to prevent the engine being damaged, the safety systems of the boiler shouldn't be relied upon to prevent you damaging it.
If you have your heating system correctly balanced, (and it was correctly designed in the first instance) you should be able to set the controls to avoid the safety system cutting in to prevent damage.

That's the way it should work, not with the boiler cutting out because the return is too hot. (or the flow/return difference too small)

I am sorry but that is not correct.

It is not a 'safety feature' but a design feature built into most(all?) CH systems in the last 2o years or so.

This from the Myson website:

Automatic Bypass Valve
What is an automatic by-pass valve?
An automatic by-pass valve is designed for use in domestic central heating systems. Its purpose is to maintain constant pump pressure within the system.
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What are the advantages of an automatic by-pass valve?
An automatic by-pass valve ensures minimum water flow rates through the boiler. It reduces system noise associated with high pressure pumps. It eliminates the need to fit an uncontrolled radiator to act as a system by-pass and it also increases system efficiency. The automatic by-pass valve also aids the operation of thermostatic radiator valves.

Also the boiler is designed to cut out when the water in the sytem is at the set temperature - that is exactly what happens.

e.g. if the room with the themostat is not at the set temperature(regardless of the TRV setting or even if a TRV is not fitted and the valve fully open) the boiler will be switching off and on as the water reaches the temperature set on the boiler and then cools.

Premier_2

With all due respect, I think we are talking at cross purposes here.

I was referring to the safety temperature limiter within the boiler itself, not the automatic by-pass valve within the system. Btw, you only need such a by-pass valve if every radiator is fitted with a TRV

In a correctly designed and balanced CH system, the water should never be so hot that boiler cuts out whilst the room thermostat is calling for more heat. If it does, it probably suggests that you have incorrectly sized radiators in your system or they are restricted in output by the TRVs or old style manual valves.

mech_2

Premier wrote: »

In a correctly designed and balanced CH system, the water should never be so hot that boiler cuts out whilst the room thermostat is calling for more heat. If it does, it probably suggests that you have incorrectly sized radiators in your system or they are restricted in output by the TRVs or old style manual valves.

I can't agree with that. Heating load isn't constant.

For some of the heating season I'm going to require very little heat (end of April or beginning of September). There's no way the roomstat can react quickly enough to stop the boiler thermostat cutting in. Even if I leave it at a setting I would normally only use for colder weather.

If I go away at christmas and come back to a cold house the heating load skyrockets. There's no way the radiators can get the air in the house up to temperature before the boiler thermostat kicks in.

Anyway, the boiler thermostat setpoint is adjustable. What kind of safety feature allows you to adjust the threshold?

Premier_2

mech wrote: »

I can't agree with that. Heating load isn't constant.

For some of the heating season I'm going to require very little heat (end of April or beginning of September). There's no way the roomstat can react quickly enough to stop the boiler thermostat cutting in. Even if I leave it at a setting I would normally only use for colder weather.

If I go away at christmas and come back to a cold house the heating load skyrockets. There's no way the radiators can get the air in the house up to temperature before the boiler thermostat kicks in.

Anyway, the boiler thermostat setpoint is adjustable. What kind of safety feature allows you to adjust the threshold?

With respect to the adjustable thermstatic control knob on the boiler, this again is something entirely different to the safety temperature limiter.

If your property take too long to warm up whether in winter or summer no matter how it is set up, again it suggests a fault in the system design (e.g. wrongly sized radiators. edit: or your boiler is oversized)

Cardew

Premier wrote: »

With all due respect, I think we are talking at cross purposes here.

I was referring to the safety temperature limiter within the boiler itself, not the automatic by-pass valve within the system. Btw, you only need such a by-pass valve if every radiator is fitted with a TRV

In a correctly designed and balanced CH system, the water should never be so hot that boiler cuts out whilst the room thermostat is calling for more heat. If it does, it probably suggests that you have incorrectly sized radiators in your system or they are restricted in output by the TRVs or old style manual valves.

Come on Premier! we are not at cross purposes, you have got it wrong!

You originally said:

Note, it is not advisable to have TRVs on all radiators in the property. A few problems can arise if you do. etc etc

I stated that is not so - and it isn't!! Most systems don't these days( last 20 years) and explained about an automatic bypass valve.(ABV)

You obviously thought that the ABV was a safety device.

The point that needs to be made is that it absolutely normal for sytems to have a TRV on every radiator and you shouldn't advise people otherwise.

In fact with TRVs an ABV makes the system work more efficiently. see the Myson quote.

As for hot water return, Mech is totally correct. You obviously set up the balance for heating the whole property with all radiators. However the majority of the time you won't have all the radiators on.

If you, say, have one radiator on, it cannot possibly disipate the heat and the boiler is switched off by the temperature of the water in the system.

Many people just have a heated towel rail on at times; how can that disipate the heat in the water?

Many CH systems don't have a wall thermostat, it was perfectly normal.

So again it is absolutely normal for the boiler to shut down because the water temperature in the system is up to the temperature set for the boiler.

Premier_2

Cardew wrote: »

Come on Premier! we are not at cross purposes, you have got it wrong!...

The only thing I got wrong was removing you from my ignore list.

Now corrected

espresso

Premier wrote: »

The only thing I got wrong was removing you from my ignore list.

Now corrected

Pity that you can't admit that you are wrong.

:rolleyes:

Cardew

Premier wrote: »

The only thing I got wrong was removing you from my ignore list.

Now corrected

It isn't important that you have me on your ignore list or not.

What is important is that you have got major issues in this thread completely wrong and have given advice that, if taken, could cost those who took that advice a lot of money.

Is Mech on your ignore list as well - as he told you you were wrong!