Another central heating question....

[chrisga]

Sorry, this may seem a bit dumb but I'm going to ask anyway.
We have a gas fired boiler which heats the water for our central heating. This is controlled timewise by a box in our airing cupboard where you set all the times you want the heating to come on and go off depending on the day. There is also a thermostat downstairs to control temperature.
We have got all of the times set to reasonable ones, depending on the day of the week, i.e. off during the weekdays as we are both out at work, comes on just before we get home etc. The heating is also programmed to go off at night when we are asleep and should according to the timers come on just before we wake up.
A couple of nights in the really cold weather though i've woken up in a sweat at about 3am with the heating on seemingly full chat.

So my question is, is there anything else somewhere on the system that controls the timings? Could there be anything on the boiler itself? I suppose i should know but dont spend much time looking round our boiler as its up in the loft and not the most accessible and just wondered if anyone had any similar experiences or good ideas.

[touching cloth]

A frost stat will override the timer, that will be my guess as to what is happening.

[spikeyhead]

Is the timer a posh programmable one or just a couple of sliders on the edge of a clock wheel?

How is it connected to the boiler? wireless or wired.

[Globs]

chrisga said:

A couple of nights in the really cold weather though i've woken up in a sweat at about 3am with the heating on seemingly full chat.

I used to have this with a honeywell battery powered programmable thermostat. Changed it for a cheaper Siemens and that has been fine.

[Simpo Two]

When my boiler timings went AWOL it was because the rechargeable battery in the programmer (to maintain settings in the event of a power cut) had failed and there had been a power cut. Does your timer still show the right time of day?

[ctdctd]

touching cloth said:

A frost stat will override the timer, that will be my guess as to what is happening.

WHS - that's what mine does.
Boiler in cold utility room fires up for a few minutes to stop itself freezing.

[Laurel Green]

ctdctd said:

touching cloth said:

A frost stat will override the timer, that will be my guess as to what is happening.

WHS - that's what mine does.
Boiler in cold utility room fires up for a few minutes to stop itself freezing.

What they both said.
Especially as in the loft - chilly to say the least in this weather.

[chrisga]

Ah ha, excellent, thanks guys.

Yes, the timer does say the correct time, sorry forgot to mention that originally but it was the first thing I checked. Im pretty sure its wired to the boiler, and its a digital one where you program the current time and day and then set all the different periods you want the heating to come on or go off.

The frost thing sounds very plausible as I thought it odd that the coldest nights I was waking up the hottest! What sort of temps does the frost thing have to get to to start the boiler up? And how long would the boiler usually remain on for once automatically fired up? Would it itself on for the whole time the frost thingy was registering that it was too cold for the boiler, so all night effectively?

Edited by chrisga on Thursday 9th December 11:35

[touching cloth]

My understanding (limited, so don't take this as read) is that you usually have a frost stat to call for the boiler to come on when cold, then a pipe stat to tell it it's done enough and the pipes are all warm (which is what you are protecting after all). It may be that you do just have a frost stat which will then call for it constantly right up until the temp around it itself raises (if this is in the loft and relying on nearby pipework to raise the temp then that could well be some time). Do you have TRVs fitted, if not this might be a nice easy solution - stick one on the bedroom radiator and it will limit the systems ability to make your bedroom into an oven.

Edited by touching cloth on Thursday 9th December 13:06

[chrisga]

Sorry, I dont know what a TRV is (temp relief valve perhaps?) let alone if we have them fitted. I have a dial to turn down the radiator temperature which i'll do if it looks like its going to be another cold night (seems completely backwards thing to do but there you go).

[scenario8]

Thermostatic Radiator Valve.

It looks a bit like an upturned egg cup with some numbers around the circle and sits next to the radiators to regulate the heat within them independently. To a degree.

You might not have them, so don't worry if the valve doesn't look as described..

[ferg]

It does sound like a frost stat issue, to be honest. They fire at 5 degrees normally, but do vary. It's another big downside to having the boiler in the loft, I'm afraid. I'm surprised it fires the heating though, we normally wire them so they fire through a bypass.

[eastlmark]

I have a similar problem to the OP. Heard the pump running last night way after the time to switch off had passed and also looked at the boiler and it was also running. I checked the timer and the lights were off, indicating it had switch off as usual so assumed a fault with the timer (shorted triac whatever) so removed the timer alltogether (it is one of those that clip onto the backplate) and still the pump and boiler were on despite there not being any connection at all to the timer. Heating however was not on, it was just the hot water. The only way I could stop it running was to switch off the power to the heating circuit altogether and deal with it in the morning.
switched it back on this morning and everything came on and worked as normal and it all swtiched off once the timer switched off. We have no frost stat for sure, no room stat as it all works on rad valves, I have had a look at the wiring and think the only way the timer can be overided is by 2 pairs of wires going to different valves fitted near the pump.
one of these is a Honeywell type with a mechanical lever sticking out the top which is set to "auto" I believe this is the valve that switches between hot water only and heating/hot water. The other valve is marked "British gas MV22Z" and I must admit I am not sure what the purpose of this one is. Both these valves have 4 (+ an earth) wires leading to them, 2 I assume powers the motorised valve itself and i am guessing the other 2 are to a microswitch to send a closed or open signal back up the junction box.
My question is, would one of these valves cause the boiler and pump to run on after the timer has switched the system off?

[Festive Ferg]

Yes.
It sounds like you have an 'S'-Plan system. Two 2-port zone valves?? They are opened by a motor energised from the timer via a thermostat and once open they open a microswitch that fires live down the ORANGE wire to the boiler. The microswitches sometimes stick after the motor has been de-energised.

Edited by Festive Ferg on Sunday 12th December 11:16

[eastlmark]

Festive Ferg said:

Yes.
It sounds like you have an 'S'-Plan system. Two 2-port zone valves?? They are opened by a motor energised from the timer via a thermostat and once open they open a microswitch that fires live down the ORANGE wire to the boiler. The microswitches sometimes stick after the motor has been de-energised.

Edited by Festive Ferg on Sunday 12th December 11:16

Orange wires, that it. So the valves are energised first which then turns the boiler on via the microswitch? I had always assumed it to be a simultaneous operation.
OK thanks for your help.

[Festive Ferg]

The five wires:

Green/Yellow - Earth obviously
Brown - Live to motor
Blue - Neutral to motor
Grey - Permanent live in to switch
Orange - Live to boiler (and pump sometimes)

No, it's not simultaneous. You'll always see that delay whilst the valve opens.

Edited by Festive Ferg on Sunday 12th December 11:30