Radiators Coming On Even With Stat At Minimum And Controller Not Calling For Heat.

[smiffffffy]

Hi all, am after advice on this boiler condition, we have had a replacement boiler in December , a new vailant , the last few nights we have as always we have turned the stat to minimum.
However, we have noticed due to being awoken by the bedroom being so hot that the boiler had come on and all radiators in the house are on.
Going downstairs to check the controller, it is NOT showing as “on” and it is outside of the two timed switch ons we have programmed that are water and heating on at 06.00 and off at 08.30, and on at 16.30 and off at 22.30.
So I am assuming this is a faulty controller.
The timer however seems to be working ok for the two timed sessions.
I am confused by the fact that if the controller last told the boiler at 22.30 to switch off heat and water that the three way valve will be closed so there is no flow in either direction.
So how is the boiler coming on and allowing water to flow to the radiators if the three way valve should be in the “no flow” positions.
The temperature has dropped outside and our boiler IS in the loft with a frost stat fitted adjacent, could this be what is happening? With the boiler taking control over the heat being turned on due to low temperatures in the loft.
We have never experienced this though with the previous Worcester boiler which also had a frost stat next to it in the loft over the last 12 years.
Is this a fault? or something that is by design with newer boilers?
Is the frost stat set too low if it is a normal operation.
Thanks in advance

[MargoTester]

We had the same problem with our boiler which is in the garage. It was to do with the frost stat setting. I would talk to the people who installed the boiler and ask them about the frost stat

[klazomaniac]

Yes smiffffy. You're caught between the devil and the deep blue sea.

The frost stat is overiding any other controls to stop your pipes freezing in the loft. (temps have been as low as 0 the last few days) A frost stat will kick in at approx 5 degrees celcius.
You can remove the frost stat. But this COULD put you in jeopardy of frozen/cracked pipework.

Are all the pipes in the loft lagged ?
And is the frost stat connected to the pipes or direct to the boiler ?

If it's connected direct to the boiler, It will be acting similar to a room stat (I bet your loft is very cold at night) It should be connected to lagged pipes via a trace tape. This will give the sensor a true reading of the pipes temp, and only kick in when the pipes are at a dangerous low level temp.

[The Builder]

As you probably know, Smiff, the frost stat is there to turn on the boiler when the ambient temp. drops.
The boiler then overrides the controller and fires up.
It SHOULD confine itself to heating the water within the boiler only.

The 3 way valve should NOT operate to allow water to the rads.
Your frost stat should be set to around 5 degrees. Below that temp. the boiler fires up until it reaches around 10 degrees. Then it switches off.

If the system is working properly, then the boiler warms up and is fully protected from freezing.

Your rads should NOT come on, regardless of the frost stat setting.
I think there's a fault somewhere that is operating the 3 way valve when it shouldn't do.

[smiffffffy]

I have been digging around and found that I may be missing a pipe stat as mentioned above.
If I I am reading other internet posts right, my frost stat kicks in when temps are low enough in the loft, this fires up the boiler and switches the three way valve to open so that the heated water flows all around the system, there should be a pipe stat connected close to the boiler on the return pipe. Therefore when the return pipe reaches an acceptable temp to avoid my pipes freezing it shuts the boiler down.
The process repeats to avoid damage.
However my system without the pipe stat is just running until the boiler shuts down through its own max temp process.
Meaning my house is being heated through the night to stifling temps.
Wasting a lot of gas.
Need to get a pipe stat fitted.