Vaillant Ecotec Plus 831 pressure problems

21 Oct 2011
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United Kingdom
Hi, we have a Vaillant Ecotec Plus 831 that was installed in 2006. The pressure keeps rising to into the red, having to bleed radiator to bring pressure down once a day. Both valves are closed on the filling loop. Now the radiators are staying on constantly even when radiator switched to off and having to turn boiler off. Can anyone offer any advise please?
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Sounds like you have two faults.
1.Pressure rising.check the expansion vessel pressure
2.radaitors on.check the diverter valve
A valve on the filling loop is letting by allowing water into
the central heating.

Remove the flexible hose to verify this.

If the boiler is off and the pressure is still rising.

It is also possible the plate heat exchanger is leaking allowing
mains cold into the central heating.
Unless you have time to spend doing tests ( which are well documented in search results on this forum ) then you may be better off getting a pro to deal with it.

These are all totally repairable problems as long as they are correctly diagnosed. Not a too massive cost but that depends on the exact cause.

Tony Glazier
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If heat off an pressure rises then probably fill loop passing could be dhw ht exch passing but rare, if pressure rises only when heat running then probably flat exp vessel, if heat gettin hot when running hot water prob duff divertor
agree with bunnyman on both these issues!! plate heat exchanger is a very uncommen fault on these!!
to confirm divertor switch of preheat and see if it happens again!!
Best get an rgi to repair this though!!!

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