Boiler anti cycling

[m0t]

I have a Worcester greenstar 28 CDI compact.

My nest didn't turn the heating on tonight in time for us to get home so it was 16 degrees rather than the 22 the missus likes.

By half 9 the house still hadn't hit the target temp which seemed odd so I went to look at the boiler. The blue light was on but it wasn't firing despite the nest telling it to.

I checked the manual and found the instructions to get into the info menu and the status was 'anti cycling mode'.

Googling indicates that this is to prevent the boiler overheating and it happens when the boiler is set to a higher heat output than the total of the rads. Is that correct?

I've checked the boiler and it's set to 24kwh on the ch. I've added up the kwh values of my rads and it comes to 13kwh.

Does this mean I should turn the ch down to 13 to prevent anti cycling, decrease heat up time and increase efficiency?

Boilers not new and I've only ever noticed this once before (when the house was heading from 12), but the rest of the time the heating comes on before we get in.

Thanks

 

[Dan Robinson]

It will help somewhat, but there could be circulation issues.

 

[m0t]

Watched it this morning and it was going into anti cycling mode every 15 minutes or so which stopped everything and let the water temp drop about 20 degrees.

I've turned the boiler down to 14.5kwh to allow for some error in my calculations and will see how that goes.

I cleaned the filter our just in case but there wasn't a lot in that (the magnetic core was still 90% white).

I suspect that the system is poorly designed. When we moved in there weren't any radiators upstairs and we paid to have some put in. It's been done in a single long run of plastic 15mm pipe so whilst it works the upstairs rads do take a long time to heat.

When decorating downstairs I've been removing lots of old dead legs that were under floors but still connected up. It looks like a mash up of different ideas from over the years (to be expected I suppose in a 30's house).

Edit: entered anti cycling mode after 40 minutes on this setting.

 

[John D v2.0]

The boiler would be modulating down to the load based on the fact that the water temperature leaving the boiler is set by a thermostat. Setting the maximum power wouldn't help that much.
If the water returning to the boiler is too hot or moving too slowly then the burner can't modulate low enough.
What is the temperature difference between flow and return? If very small isit just not enough heat demand, if high then you have poor flow

 

[m0t]

Just checked and it was fluctuating between 6-10 degrees at 65 degrees flow.

 

[John D v2.0]

That's not bad, a bit low so it could be a combination of flow and low demand.
Anti cycling isn't a bad thing in itself, it's a bit like when you run your microwave on low and it just kicks in and out.
Are the rads cooler than the return temperature back to the boiler? Could be bypassing through one rad and be poor flow as you say.
The experts might have better ideas than me

 

[m0t]

No, the rads get hotter than the return (based on the back of my hands).

The main problem is that it was cutting in for 5 minutes every 15 and the flow temp had dropped over 20 degrees by the time it started back up again. I'm assuming that was why the house wouldn't get up to temperature properly.

Since cleaning the filter and changing the output it did heat up to 22 without an issue.

Before I discovered the anti cycling issue I'd wondered if my rads were undersized but they are all quite large and the house is clad in external insulation.

The other possibility is the temp sensor in the nest has failed. It's a rubbish bit of kit so it wouldn't surprise me.