S plan fully pumped boiler switch off every 2-3 minutes

Still in Limbo!! I replaced the programmer today from Drayton 740m to Heatmiser tm4-ts....still no luck...boiler shuts off every 1 or 2 mins....Can I replace the pump? or 2 port valves? Any advise will be appreciated

Apparently, they can feed low voltages back to boiler PCB's and cause firing...

As said, just a thought if everything else is proved oakiedoakie


That's very interesting. Fortunately my 'German' boiler doesn't suffer from that problem, but it's not the same model as Badri's, will put this one away in my brain though ;)
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Why did you replace the programmer? It has nothing to do with the cycling!
Anyway, if you are still getting the cycling it is likely a low flow problem, provided you have set the ABV as I said. Some photos of your new pipework might help.
Why did you replace the programmer? It has nothing to do with the cycling!

I thought it might be faulty programmer and this programmer is cheap and I had this as spare and thought will give it a go!! it does the same work as T740m any way...
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Guys we update!! after Air bleeding the pump, zone 2 with 28mm 2 port valve zone started working with no issues boiler was on for 1hr.30mins without switching off.....however boiler is still switching off for zone 1 and 2 which runs off 22mm port valve any advice please
for unkown reason problem has re-occurred for all the zone again.. boiler again switching on and off every 2-3 mins!! Help please!!!!
Poor circulation. Check pump set to 3. Otherwise blocked pump impeller or slow running pump
This is definitely a poor circulation issue, either the system is airlocked, sludged or the pump is no good.

1) Take a note of the position of all the lockshield valves - open them all right up and see if that solves the issue temporarily.

2) Turn flow temp on boiler down low. Close all the rads on one zone, except one. Run the system on this one rad only with the pump on max. Repeat with all other rads and all zones then return the system to the state described in 1). Turn flow temp up.

3) Do I recall that this is an open vented microbore system? Hope that it isn't sludged up.

5) Change pump if necessary for a UPS2 15 - 50 / 60 (That's the model number, not two different options). Use the cable it comes with.

Edited for typo.
are air vents fitted at the highest point im the system ? just sounds air locked to me , try fitting auto air vents & balancing the system up
Hello all thanks very much for help specially Mogget. I managed to source out the root cause....it turned out that ABV is faulty. I.e. it was not closed properly and water was pumped back to boiler before it reach to radiators!! I have ordered Mayson this time Honeywell has been returned. I have fitted 15mm old gate valve and balanced system as required...all the zones are working without boiler switching off!!! I am also returning Drayton Mitime programmer and settling to Heatmiser 4 channel programmer with wired cylinder stat and room stat!!
And there was me thinking it may, just may be a 'fault' on the motorised valve, acknowledged by Honeywell Techies, that affects some (and in their words, "German") boilers, causing 'cycling'.

Cured apparently by positioning a capacitor in the wiring centre.

(the BG330 is a Glowworm - owned by the Vaillant - German- parent group, and maybe considered the Vaillants ugly sister)

Just a thought.


You wouldnt get this fault on an S-plan only Y-plan and its mostly older worcester greenstars that suffer from it.

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