Ecotec Plus 831 switching itself on

[Jon0781]

Hello

We have a Valliant Ecotec 831 in the loft. A few times last winter and more regularly this last week or two the boiler switches itself on and stays on. It's connected to Hive and that is switched off on the schedule, the only way to reliably stop it heating it to turn off the boiler directly or gas. Happening particularly overnight and obviously it's baltic this week...

We had a heating engineer out yesterday who didn't even look at it. He just said it could be PCB or diverter valve but no way to tell and consider Valliant one off repair service.

Any other thoughts/suggestions? I'm wondering if frost protection is kicking in then not turning off?

 

[Mottie]

How long does it stay on for?

 

[Jon0781]

Hours, came on the other morning at 1am and stayed on til I woke up at 5ish.

 

[Mottie]

Ah, well, probably something to do with the frost protection and could be the PCB not switching off or the diverter valve or even something else. Vaillant one off repair maybe your best bet - they'll possibly change everything that could cause it just to be on the safe side! Come back and let us know how you get on - may help someone else in the future.

 

[DP]

When someone without a look or taking the cover off the boiler can proclaim pcb or diverter as being faulty, he most Likely is a repairer who fixes boilers by changing parts, one part after another until boiler is function or you give up

 

[CBW]

Did the radiators heat up? Do you have the preheat/comfort mode on? Could be frost setting, but to run for 4 hours seems a lot. Is the property on zonal heating?

 

[Jon0781]

Did the radiators heat up? Do you have the preheat/comfort mode on? Could be frost setting, but to run for 4 hours seems a lot. Is the property on zonal heating?

Yeah all the radiators were on. No comfort mode set and not on zonal heating.
Wondered if frost mode is kicking in and then a fault is stopping it turning off.

 

[CBW]

Could be frost thermostat built in, but doubt that would heat the rads. Do you have a timeswitch 150?

 

[Harry Bloomfield]

Yeah all the radiators were on. No comfort mode set and not on zonal heating.
Wondered if frost mode is kicking in and then a fault is stopping it turning off.

I have a 418 fitted, and my log suggests it has burnt no gas at all during any night this past week, as a result of the house needing heat, or the boiler firing in frost mode.

 

[stem]

Could there be a remote frost thermostat somewhere?

They are installed where there is a risk to pipework freezing, and override all other controls (i.e. Hive) to fire up the heating when the area they are located in gets down to a few degrees C. Because the area in question isn't heated it would keep the heating running until the area warms naturally. So, the smaller pipe thermostat shown on the left is fitted to the return pipe to the boiler and wired in series with the frost stat to switch the heating off when the water gets slightly warm but not hot. The idea is that it will be just enough to stop the pipes freezing, but won't get hot enough to heat the house.

Sometimes the pipe stat gets inadvertently turned up so doesn't switch off when it should, and sometimes there isn't one fitted at all, so the heating just keeps going until the area where the frost stat is located rises enough to switch it off.

 

[Jon0781]

Could there be a remote frost thermostat somewhere?

View attachment 329701

They are installed where there is a risk to pipework freezing, and override all other controls (i.e. Hive) to fire up the heating when the area they are located in gets down to a few degrees C. Because the area in question isn't heated it would keep the heating running until the area warms naturally. So, the smaller pipe thermostat shown on the left is fitted to the return pipe to the boiler and wired in series with the frost stat to switch the heating off when the water gets slightly warm but not hot. The idea is that it will be just enough to stop the pipes freezing, but won't get hot enough to heat the house.

Sometimes the pipe stat gets inadvertently turned up so doesn't switch off when it should, and sometimes there isn't one fitted at all, so the heating just keeps going until the area where the frost stat is located rises enough to switch it off.

I don't want to speak too soon, but this may be spot on! Yes there is a frost stat and pipe stat, I've turned down the temperature on the pipe stat so will see over a few days if that makes any difference. If not, will dig a bit deeper and see if wiring etc is correct.

Will update either way so may be of benefit to someone else

 

[Jon0781]

Could there be a remote frost thermostat somewhere?

View attachment 329701

They are installed where there is a risk to pipework freezing, and override all other controls (i.e. Hive) to fire up the heating when the area they are located in gets down to a few degrees C. Because the area in question isn't heated it would keep the heating running until the area warms naturally. So, the smaller pipe thermostat shown on the left is fitted to the return pipe to the boiler and wired in series with the frost stat to switch the heating off when the water gets slightly warm but not hot. The idea is that it will be just enough to stop the pipes freezing, but won't get hot enough to heat the house.

Sometimes the pipe stat gets inadvertently turned up so doesn't switch off when it should, and sometimes there isn't one fitted at all, so the heating just keeps going until the area where the frost stat is located rises enough to switch it off.

Another question if you don't mind!

I've replaced the pipe stat (L641b1004) on the return pipe. I've tried setting it to both 10 and 20 degrees and the pipe heats up to what feels reasonably warm yet the boiler doesn't cut out automatically when temperature reached. If I turn the temperature dial down manually by a mm or so then the boiler cuts out as it I'd expect. Wiring contacts C and 1 have been used.

Any thoughts, I definitely think this is the issue but can't seem to get past this last hurdle!

 

[stem]

The pipestat will only work in conjunction with the frost thermostat. What that means is that when the normal heating controller [Hive] is calling for heat the pipestat won't do anything. From your last post though I think you know this already. Just make sure the heating is off at the Hive when making any tests of the frost protection system.

As for the wiring: C and 1 are the correct terminals, but the two thermostats must be wired together in series, as per the diagram below. Both have to be 'on' (calling for heat) to start the boiler, but if either one is 'off' (satisfied) the boiler is off.

 

[Jon0781]

The pipestat will only work in conjunction with the frost thermostat. What that means is that when the normal heating controller [Hive] is calling for heat the pipestat won't do anything. From your last post though I think you know this already. Just make sure the heating is off at the Hive when making any tests of the frost protection system.

As for the wiring: C and 1 are the correct terminals, but the two thermostats must be wired together in series, as per the diagram below. Both have to be 'on' (calling for heat) to start the boiler, but if either one is 'off' (satisfied) the boiler is off.

View attachment 330017

Thank you.

Yeah so when I tested it, I switched the hive off and turned up the frost stat to 30 degrees which in turn kicked the heating in.

The pipe stat was set to 10 degrees on the return pipe but it only turned the heating off when I turned the pipe stat dial down a fraction despite the pipe being fairly warm. I'm guessing this means it's wired correctly as it is turning the boiler off, just not when it hits the temperature.

Will check the wiring too but may need to get a sparky in to be honest.

 

[stem]

That sounds as if it is wired OK then. But there are a few things to consider:

1. If there is an external by-pass with a pump overrun, then the pipe will continue to receive heated water until the pump overrun times out. Although if this were the case it wouldn't stop immediately when you turned the pipe-stat down......unless the overrun just happened to timeout as you did it.

2. It can take a while for the pipe-stat to pick up the heat from the pipe, and it could be possible that the pipe can heat up quite suddenly, so if it took a minute to register it, the pipe might continue to warm quite quickly before the pipe-stat goes off.

3. If the pipe-stat is located in a very cold position where the ambient temperature is only a couple of degrees, that may have a cooling effect on it.