Boiler coming on for just a few seconds

[paulockenden]

S-Plan system, wired as per the official diagram.

I've noticed that sometimes the boiler will power up, only just long enough to ignite (which takes about 30 seconds), and then instantly powers down again (I just ran upstairs to check and both relays are off, so it's not the boiler's own thermostat switching it off).

Is this deliberate? If so, what's the point of it? I guess it means the pump runs for a few seconds, but I'm not convinced this frequent short-cycling of the boiler can be that good for it.

P.

[top brake]

S-Plan system, wired as per the official diagram.

I've noticed that sometimes the boiler will power up, only just long enough to ignite (which takes about 30 seconds), and then instantly powers down again (I just ran upstairs to check and both relays are off, so it's not the boiler's own thermostat switching it off).

Is this deliberate? If so, what's the point of it? I guess it means the pump runs for a few seconds, but I'm not convinced this frequent short-cycling of the boiler can be that good for it.

P.

Check the installer settings, system devices, heat demand

should state No boiler relay

[paulockenden]

Check the installer settings, system devices, heat demand

should state No boiler relay

Yep, it does.

The professional installers had originally double-bound the heating relay so it was a boiler relay as well, but after they left I corrected that.

P.

[top brake]

Yep, it does.

The professional installers had originally double-bound the heating relay so it was a boiler relay as well, but after they left I corrected that.

P.

Did you clear existing bindings on the BDR91s?

[paulockenden]

Did you clear existing bindings on the BDR91s?

Yup. Can confirm that they only come on with the appropriate demand now. Prior to that the heating relay would open for hot water too, because it also thought it was a boiler relay.

P.

[garmcqui]

This extremely short boiler demand problem seems to be quite common, I had it too.

No amount of unwinding and rebinding would fix it, so in the end I reverted to configuring one BDR91 as boiler relay just so I could set the minimum on time and cycle rate.

[paulockenden]

Saw a couple of examples today where the boiler wasn't just short cycling, it was 'nought' cycling! i.e. the boiler powered up, then the gas valve opened and the ignition started to spark, but the power switched off before it even got a chance to light!

I know this is probably something to do with TPI, but this behaviour can't be right.

I'd suggest that the minimum boiler on time setting shouldn't only be visible when you have a boiler relay in the setup, it really needs to be there with an S-Plan setup too.

Right now I'm just wasting unburned gas!

P.

[top brake]

Saw a couple of examples today where the boiler wasn't just short cycling, it was 'nought' cycling! i.e. the boiler powered up, then the gas valve opened and the ignition started to spark, but the power switched off before it even got a chance to light!

I know this is probably something to do with TPI, but this behaviour can't be right.

I'd suggest that the minimum boiler on time setting shouldn't only be visible when you have a boiler relay in the setup, it really needs to be there with an S-Plan setup too.

Right now I'm just wasting unburned gas!

P.

This isn't normal at all.

Have seen it when there is an issue with a HR92 and when BDR91 too close together

Process of elimination to identify the cause.

[paulockenden]

Sounds like I'm not alone, and the TPI PDF suggests this kind of behaviour.

There's no BDR91 and HR92 close together. The only slightly naughty thing the 'professional' installers did (*) was to mount the DHW BDR91 and the tank stat box next to each other. But I struggle to see how this might be the cause of the problem, especially when the demand when it's happening seems to be heating rather than DHW related.

P.

(*) other than not programming the system properly, of course!

[paulockenden]

@garmcqui - Did you try fooling the system into thinking you had a boiler relay, adjusting the minimum on time parameter, and then removing the boiler relay? I thought it might be worth a try, but it sounds like you went through a few options already...

Ta.

P.

[top brake]

Eliminate all incorrect installation aspects please. Also need pictures. Thanks.

Sounds like I'm not alone, and the TPI PDF suggests this kind of behaviour.

There's no BDR91 and HR92 close together. The only slightly naughty thing the 'professional' installers did (*) was to mount the DHW BDR91 and the tank stat box next to each other. But I struggle to see how this might be the cause of the problem, especially when the demand when it's happening seems to be heating rather than DHW related.

P.

(*) other than not programming the system properly, of course!

[paulockenden]

I've sent you a PM regarding certain aspects.

P.

[erik]

FYI: I've seen the bdr91 turning on a few times for only 30 seconds or so, even when minimum-on-time is set to 2 minutes.

But usually only right after I had made a change to setpoint. I assumed because the bdr91 was still going on because of the old setpoint and then instantly going off because of the new lower setpoint.

[top brake]

FYI: I've seen the bdr91 turning on a few times for only 30 seconds or so, even when minimum-on-time is set to 2 minutes.

But usually only right after I had made a change to setpoint. I assumed because the bdr91 was still going on because of the old setpoint and then instantly going off because of the new lower setpoint.

makes sense

[f1arp72]

@paulockenden: Did you find out what may of been causing your problems ? I have a similar thing where the boiler fires up but doesn't stay on long enough to have any effect on the water temperature inside the radiators, then turns off again. It's a completely pointless exercise and just anther reason I have lost all confidence in this system. All solutions seem to resolve around resetting system and setting it up again, but I've done it 4 times, and am 100% convinced the system is set up correctly.

As I type this, I just heard boiler fire up for 30 seconds and switch off again as the DBR91 called for heat, then turned off again after 1 minute.