Vaillant Eco tech 428 playing up

[chelsea_khb]

I have got a Vaillant eco tech 428 heat only boiler which has been installed to a pressurised heating system. When I put the hot water on 'auto' at the programmer the boiler will fire up and heat up the hot water cylinder then after a while the boiler will go out once its reach temp and the pump over run will kick in. The problem is that it then fires up again a few minutes later reaches temp (roughly 65 degress) rather quickly, then goes to pump over run. This will keep happening say every 5 mins. This cant be right? I dont whats causing it to fire up so frequently, is it the boiler, three port valve, cylinder stat, by pass valve not working correctly. I know these boilers dont like air but system doesnt seem to have any air in it as its very quite and has auto air vents fitted at highest points. If anyone has any ideas or solutions to what the problem might be, please let me know as its driving me mad, just cant get me head round it. Cheers Kris

 

[thunderboxtech]

check wiring first, sounds like you have got a switched live going to the boiler when the cyl stat is satisfied.

 

[chelsea_khb]

Ok will do, thanks for the quick reply

 

[bell824]

press the I button on the boiler



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[RoryD]

Are you sure the cylinder has reached temperature and not the Boiler? Ensure the stat on the boiler isn't set low... it won't save gas quite the contrary, if it is low then the CHB will satisfy long before the cylinder stat giving the effect you're having. I come across this frequently.

 

[bell824]

sorry mod new to the forum maybe my reply was harsh ask the question and i will answer openly.

 

[chelsea_khb]

check wiring first, sounds like you have got a switched live going to the boiler when the cyl stat is satisfied.

Got a heating engineer to check the wiring and everything seems fine in that department. He said that there is a switch live going to the boiler but thats normal for these boilers as they wont work without one. Switch live wired to Terminal 4 on the boiler. Any suggestions?

 

[chelsea_khb]

Are you sure the cylinder has reached temperature and not the Boiler? Ensure the stat on the boiler isn't set low... it won't save gas quite the contrary, if it is low then the CHB will satisfy long before the cylinder stat giving the effect you're having. I come across this frequently.

The boiler stat is set at 70 degrees, the cylinder stat set at 60.

 

[chelsea_khb]

press the I button on the boiler



There should be no need for pm's
All advise should be given on the open forums so others can benifit,comment and discuss openly

Thank you

Mod Team

There is no fault code the display reads S.7 which is pump over run

 

[Eddie Charlton]

the question to be asked is, does it do it with central heating and hot water switched off. if all ok on heating then suspect external control/ or mortorised valve for hot hot water if S plan.

 

[Rossi46]

Range rate to match coil load.

 

[biblet]

Not sure what the comment 'Range rate to match coil load'?
I believe I have these symptoms of the original comment, namely:
Vaillant System boiler, ecotec plus 428, vented/open, driving CH and HW. Two motor valves.
Has been installed and run for 18 months with no problems. (Replacement boiler and tank, existing radiators flushed).
CH and HW are still fine and operational, so the only problem is the pump keeping us awake at night.
When there is no call for CH or HW, the pump is unnecessarily run for 5 min with 1-2 min 'rest'.
At the start of each 'run', the boiler fires up but just for a couple of seconds.
Display during these 'runs' is S.7, 'Pump over run'. Radiator icon flashes (in user manual 'anti-cycling mode active'), and tap icon and pump icons are displayed.

Can anyone make a suggestion - is a sensor failing, blockage somewhere?
Thanks,
Steve

 

[brightcrow]

biblet

Reckon, your boiler should still be under warranty, worth giving Vaillant a call. Does sound like unusual behavior but the boiler controls the pump directly so like you say could be overheating due to slow flow rate(ie blockage) or a sensor failure.

 

[biblet]

Hi, thanks for that. Regrettably it's a 1 year warranty, though they ought to provide some telephone assistance. Overheating due to slow flow/blockage sounds unlikely if normal operation works. Perhaps an internal temperature sensor is reporting too high a value though?

Steve

 

[sparkygas]

the pump on your system needs to be supplied from the 230v pump terminals on the 428's pcb. If not you get exactly the problems you describe because these boilers need a lot of over run. If the pump is a long way from the boiler its probably easier to move the pump to a location near the boiler than do a long wiring run.

 

[Anton]

It's not kicking in for frost protection is it?
If a temperature sensor has gone out of range that might cause the operation of the pump and then the boiler outside the programmed times.

 

[biblet]

Thanks for your comments, I am impressed that no-one wrote 'it must be the PCB - replace it' !!
Given that the boiler fires up for a few seconds, then turns off and overruns for the set 5 mins, and this is all outside programmed times, then the frost protection feature could be being started up, and then turned off as it discovers, perhaps from a different sensor, that the water is way above frosty. Does anyone know which sensor to look at? (I am an electronics and software engineer, with plenty of measuring gear!)

 

[Anton]

You really need to make sure that you have no 240v switched live feeding the boiler when it does what it does.
A sticky end switch on one of the zone valves could give the same symptoms. Each zone valve has a microswitch which puts the power through to the boiler SL when the zone valve is open. If a switch is stuck when the zones valves are shut, this can cause the problem you describe.