Central Heating Timer Intermittent

[Plasmaduck]

Hopefully someone can shed some light on this issue.

I went to a clients house, he claimed that since an electrical storm, his heating timer and operation was intermittent with the display not always coming on and displaying info.

As the obvious choice and the only part with static sensitive parts was the timer (Smartfit 7 day with built in thermostat), I ordered a new unit and all was fine for a week. He called me today to say that today it was set at 21 degrees, but was still keeping the CH on at 24 degrees and climbing. 

My first thought is perhaps the power source is arcing and therefore not always supplying hence the blank display and possible corruption with power spikes. Second is that maybe voltage is feeding back through the two wires at back of the timer, possibly from the boiler? Last would be that the new timer is also faulty?
Whilst typing this out, it doesn't seem possible that there are only two wires to the unit, although between the timer and its backplate, there are only two prongs that connect the two together. There must be hidden wires as at least two would be needed to power the timer, and at least another two to switch a signal to the boiler.

Any thoughts would be appreciated

 

[ProDave]

It sounds like you are describing a programmable thermostat, rather than a conventional boiler programmer.

Those are often battery powered and indeed just have two contacts being a relay contact to call for heat from the boiler.

If I'm right and it's battery powered, then you can detach the unit from it's backplate and the display and everything should still work. If the display is going off like that, then it has to be a faulty unit or dud batteries.

Also check with the unit detached from the back plate that the boiler has indeed turned off. It could be a faulty motorised valve that's stuck on hence calling for heat all the time.

 

[Plasmaduck]

Thanks Prodave. 

I think I have sussed out the problem - a plug in system is all new to me, plug in motorised valve, thermostat etc etc. I'm used to old school where we get a meter out and measure voltages! The Timer unit seems like it is powered by a remote base unit, as far as I can see, this can be the only thing left that can cause the problems described. 

The base unit gets the power from the mains, feeds the timer and probably has a built in back up battery also. I'm used to having motorised valve problems but have never known one to affect the display on a timer, so fingers crossed, logic would dictate that the base unit is at fault :s

 

[ProDave]

Post a picture of what you have, otherwise we are guessing.

 

[roys]

Might be related, I have one of the programmable transmitter / receiver type stats (salus 500rf), it had worked perfectly for the last 2 years until I came back from a weekend away a couple of weeks ago, opened the door to my house and the first thing I noticed was the wave of heat hitting me with the central heating being on full tilt without the remote unit demanding it. I had set the remote unit to default frost protection which means it should have only come on at below 5 deg C. The house was now at about 25 deg C.

So I tried a couple of things, reprogrammed the unit after pressing the wee tiny recessed reset button. Changed the batteries, all appeared to work for about an hour and then the boiler would click on by itself without a demand call for the remote unit.

Solved it in the end by changing the default address on the transmitter and receiver with the jumper switches. I can only presume a close neighbour has fitted some new wireless device in their house. By coincidence I have noticed a new network router showing up on my ipad recently.

 

[steptoe]

OK,

I replaced one of those plug and play systems a while back,

you canNOT simply replace the programmer with a normal programmer,

you canNOT simply replace a valve with a normal valve

you canNOT replace anything with a NORMAL ANYTHING

it all has to be the same system

me and plumber ripped the whole lot out and replaced everything with PROPER stuff.

that, my friend, is the ONLY proper solution, rip it all out and replace it with a PROPER system, not some snake oil they have been mis-sold by the installer.

 

[Plasmaduck]

ProDave, it is the Honeywell Smartfit 7 day timer and base which is located in the airing cupboard - nothing specific to photograph.

Steptoe, that is exactly right, all valves etc plug in and are low voltage. I agree that the original basic system is the best, but I was doing this as mates rates and really hope the base unit is the only other thing in the circuit that could be at fault. Live and learn, don't do mates rates for people that end up wanting the moon on a stick, which is what I've ended up with!

I tried to post a link but as I've not yet had 10 posts, I'm not allowed to!