Thermostat and timer for System boiler

[sxturbo]

Hi All,

i have just moved house and it currently has a Main system boiler HE installed, its approximately 10 years old and the heating controls are the same age.

The wall mounted thermostat doesn't seem to click off when the desired temperature is reached, we suddenly start to notice we're melting, and have to turn it down manually.

we normally have the house set to 20, and have a room thermometer for baby and thats showing 22 degrees and the heating still pumps, have tried a couple of thermometers in the room and the same results, so i'm pretty certain the stat is faulty.

currently installed is a honeywell hot water and heating control, i was hoping there is something more modern i can replace this with.

at the moment i have 3 options, constant, once per day or twice per day for the heating and the hot water. the hot water isn't a problem twice a day works well but a bit more control over the heating would be beneficial.

 

[oldbuffer]

You are likely to have either 2 x two port valves or 1 x three port valves to direct the flow of hot water from the boiler to either or both of the hot water and central heating circuits.

When either the room thermostat or the hot water cylinder thermostat detect(s) a need for heat the thermostats puts a voltage onto the motor which drives the appropriate valve. When the motor drives the valve to the open position, the valve triggers a microswitch which tells the boiler heat is required, whereupon the boiler (should) fire.

If the microswitch gets stuck it can cause the boiler to run non-stop. Room thermostats are usually pretty reliable, the motorised valves less so. My first instinct would be that the central heating two port valve, or the three port valve, has failed.

 

[sxturbo]

You are likely to have either 2 x two port valves or 1 x three port valves to direct the flow of hot water from the boiler to either or both of the hot water and central heating circuits.

When either the room thermostat or the hot water cylinder thermostat detect(s) a need for heat the thermostats puts a voltage onto the motor which drives the appropriate valve. When the motor drives the valve to the open position, the valve triggers a microswitch which tells the boiler heat is required, whereupon the boiler (should) fire.

If the microswitch gets stuck it can cause the boiler to run non-stop. Room thermostats are usually pretty reliable, the motorised valves less so. My first instinct would be that the central heating two port valve, or the three port valve, has failed.

Thanks for that, will investigate further over the next few days.

whats the best way to test the valve, is it just a case of turning the heating on and listening to the valve?

 

[ianmcd]

easily tested , post some pics of what you have and we will tell you how to test

 

[sxturbo]

Its a honeywell 3-way mid point valve.

 

[sxturbo]

Have checked the system, and it transpires that everything is working as it should, we were just used to a very cold house before.

I have put the thermometers next to where the thermostat is and they read vaguely similar I think the stat is a degree or so out, but have now compensated for this.

Having looked around I will be purchasing a nest setup so I have better control of the heating and hot water.

 

[stem]

As you say, when you turn the room thermostat down manually, it clicks and switches the heating 'off', then that shows that the motorised valve and it's associated microswitch are working. It is the thermostat that is at fault for not switching off when it should.

If it's an old design room thermostat with a dial that is mechanically operated as your description suggests it could be, then they often do get less accurate as they get older.

Sometimes they are incorrectly wired in too. They have a tiny heater inside (aka an accelerator) that is there to help overcome their mechanical inaccuracy. This heater should be connected so that it switches 'on' and 'off' with the thermostat, but sometimes they connected so as to be on all of the time, or none of the time.

A modern electronic thermostat will rectify that.

 

[Grumpy Gasman]

Sometimes they are incorrectly wired in too. They have a tiny heater inside (aka an accelerator) that is there to help overcome their mechanical inaccuracy. This heater should be connected so that it switches 'on' and 'off' with the thermostat, but sometimes they connected so as to be on all of the time, or none of the time.

For the accelerator to function a neutral is required , if no neutral input the accelerator won’t function.
How would you enable the accelerator “to be on all of the time”? Unless of course the call for heat is 24/7.

 

[stem]

How would you enable the accelerator “to be on all of the time”?

By connecting the accelerator across the live supply (instead of the switched live) and the neutral. That way it is 'on' all of the time the heating is on, thus preventing the accelerator working as it should by switching on and off with the thermostat.

It wouldn't have any effect at all on the operation of the heating when is was 'off' at the programmer / timeswitch as the heating isn't operating either. So is irrelevant.

 

[Grumpy Gasman]

It wouldn't have any effect at all on the operation of the heating when is was 'off' at the programmer / timeswitch as the heating isn't operating either. So is irrelevant.

Exactly.
So not on “all of the time”.

 

[stem]

That is quite correct of course. Wired that way it will be on all of the time that the heating is. Which I think you know is what I meant

The OP's post was relating to the inaccuracy of the room thermostat, in that it wasn't accurately controlling the heating. Which of course would only be when the heating was switched on.

 

[fixitflav]

Have checked the system, and it transpires that everything is working as it should, we were just used to a very cold house before.

I have put the thermometers next to where the thermostat is and they read vaguely similar I think the stat is a degree or so out, but have now compensated for this.

Having looked around I will be purchasing a nest setup so I have better control of the heating and hot water.

A friend of mine had a Honeywell T6360 roomstat behaving like yours. I found it had no neutral so thought that could be the problem, but when I provided one it made no difference. Turns out it's a filled system - volatile fluid in an expanding bellows, which had leaked. So he replaced it with something else.
If you're thinking of going for a Nest I would look at the many posts on this forum about queries and problems with that and similar systems.
Just out of curiosity I was looking on the web the other day trying to learn a bit about them, and while there was plenty of BS it wasn't at all clear to me what it actually does, apart from switching things on and off, which a traditional timer does OK. Perhaps it's just me.

 

[sxturbo]

A friend of mine had a Honeywell T6360 roomstat behaving like yours. I found it had no neutral so thought that could be the problem, but when I provided one it made no difference. Turns out it's a filled system - volatile fluid in an expanding bellows, which had leaked. So he replaced it with something else.
If you're thinking of going for a Nest I would look at the many posts on this forum about queries and problems with that and similar systems.
Just out of curiosity I was looking on the web the other day trying to learn a bit about them, and while there was plenty of BS it wasn't at all clear to me what it actually does, apart from switching things on and off, which a traditional timer does OK. Perhaps it's just me.

Yeah none of them really do much more than be digital timers.

I haven't taken the stat apart and checked the wiring as yet, but it works just the temp is out of calibration.

 

[fixitflav]

Yeah none of them really do much more than be digital timers.

I haven't taken the stat apart and checked the wiring as yet, but it works just the temp is out of calibration.

If it's like mine the knob is on splines. You can pull it off, turn it so the pointer lines up with the actual temperature, and push it back on.