Valliant ecotec plus 418 slow to startup/heatup CH

Hi

I have a 418 heat only boiler, external 3 way valve and running Y plan. No air in system and running Fernox F1 since new. Also magnetron on return next to boiler, hardly any deposit when checked every 6 mths.No ambiant temperature controls fitted. All Y plan valve working correctly and pump running fine and also bled.
On firing the CH with room stat well up up the boiler fires fine on what sounds like full power for about 1 min, I can see the temp rising to approx 45 deg. It then cuts down but is still burning but VERY slowly (can see gas meter moving). It stays like this for approx 6- 7 mins before firing on full briefly for less than 30 secs when it goes to about 53. It continues like this and the rads do eventually get hot but it can take nearly an hour. I think this is like a slow start. D.0 is set to 70, D.2 is set at 14, When it initially starts up the flow temp goes to 32 ish and the return is approx 23...both change gradually. I have looked on forum but nothing obvious on how to reduce this slow startup. I can see that D7 is possibly associated with this..its set at 53. Think it was like this last year but as working not a major issue but now retired. Any help please on what may need checking/adjusting

Isn’t d0 the setting for the maximum power in kW on all of these Vaillant boilers? I would have thought it’s range would be adjustable from very roughly 5kW to 18kW and reading the above I’m not sure what yours is set to at the moment.
It is normal for the boiler to run at medium power for a short time on firing up and after that it will be influenced by the water temperature / target and limited by the setting of d0.

Thanks Jackthorn, My error on D.0 its set at 14 e.g 14Kw. Have tried upto 16 but made no noticiable difference. The temp on front panel is set at 70. I appreciate that they run lower initially but this appears too long. When it does fire on full its a very short period (seconds) till it gets to 70 then shuts down to trickle but the window of this is as stated many minutes hence it takes nearly an hour to get rads to a reasonable heat output. My concern is that this will not be sufficient between room stat demand eventually being met then when room cooled switching back on and taking another hour to climb back up. There must be something that I missing and needs adjustment. Any other help greatly appreciated.

I have the same boiler and when tinkering with it once, I had the same problem as you. Check what your max output is set at - I have mine at 16kw. I had the trouble when I had mine set to 'Auto'. Apparently that isn’t too good on these. Also, having the external pump on the lowest setting did it too - I now have mine on speed 2 (of 3). Mine is set at 65° on the front panel. What room thermostat do you have?

When it is running at higher power is the water temperature shooting up quickly towards 70C?
If so you likely have a flow restriction which is causing the boiler to back off the power for a while to avoid overshooting. On my Vaillant I need to have the pump set to max to avoid similar problems.

When the boiler is running press the "i" button and see what s code is showing, do you have any idea how many kws you need to heat your home ?

Hi All

Had time today to get back to you all. D0 is set at 12 now. D2 initially on default at 20.
Last night and with room stat up and CH only, boiler fires with S2, then S3,then S4. full burn for approx 40 sec to one min upto 70 then S53 and hour glass on display. D40 and D41 were 41 and 23. Boiler continues to run like this on very low burn with temps creeping up by 1 degree till 9 mins then a very brief burn of 4-5 secs then back to S53 when temps are 45 and 26. At 19 mins another burn up to 70 and back to S53 and temps 53 and 34. this continues untill at 42 mins when temps are 60 and 40 boiler has two longish burns and after there is no timer or S53, boiler keeps giving full burns of 10 secish regually and radiators rise from tepid to hot after just over the hour.

Today I have upped the Grundfos UPS 15-50 pump to setting 3 from 2 and reduced D2 to 6, also D0 to 10. Repeated above and mostly same as above but I think marginally improved to hot rads in just under the hour
I dont know what my KWs are but I have listed the Rads below. D double, S single. Only one has a single fin on and marked that as P+. Hot water cylinder is 900x450. This is near boiler (GF) and 1st floor.
D1350x700, D1000x700, D1000x600, D1600 x700, D1600x600, DP+1300x750, S1130x700, S1300x600.1400x600 towel rail. All have TRVs with exception of largest and smallest and towel rail.

As I say system has been flushed and always treated with Fernox F1. On draining clear water except the last cup and only very slight and it has magnetron on return next to boiler that is checked every 6 mths but has very little on magnet when cleaned.
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Thanks for any help

I would stick another pump in.

Put a new Grundfos UPS3 pump in at weekend and put on 3rd setting. No change at all on first day but then on Sunday suddenly the rads were hot in 20 mins and been fine since. I think some sort of partial blockage on return flow that new pump has cleared. Fingers crossed stays so.
Many Thanks to all who assisted me