Weird behaviour Vaillant

[Robert]

Glad the D.000 change helped I have the Pump set to Comfort mode (1) Also D.002 Anti cycling time reduced from 20 mins to 6 mins. This better reflects the way my EVOHome thermostat controller works and the needs of my large Victorian house spread over 4 floors and its room occupancy.

In hindsight I should have gone with the less Green Valiant ecotech plus boiler. I do think these super green boilers are trying too hard to minimise CO2 emissions with programming algorithms which no-one understands. While probably suitable for a well insulated house with most rooms in use all the time they seem ill suited to older larger properties.

[John Rumm]

Ah, now that is going to run up against the anti cycling timer in the boiler that is designed to eliminate short cycles... (there is a timer you can configure - d.2 - it defaults to 20 mins according to manuell, but can go as low as 2)

Yup, that wounds like a decent plan.

If you are going to stick with a traditional on/off style stat, then something like the Horstmann centaur stat is a good programmable 7 day one, with 6 (user configurable) time slots per day. But no fancy optimising or PWM style shenanigans on the output.

(personally I would look at one of the Vaillant ebus stats since that does the job better and makes the whole thing easier to setup and use)

What make / model of cylinder is it? Do you know what the max transfer rate of the HX coil in the cylinder is specified at?

Since it sounds like it might be quite a low recovery rate for an unvented cylinder. (My 210L Unistor can take heat in at a maximum of

22kW, and so it pretty much takes the full boiler output for the bulk of the re-heat). 1/4 to 1/3 of 18kW sounds more like a traditional cylinder with a 5 - 6kw limit on heat transfer.