Vaillant 637 with pressure issues

[JonWebb]

Hi there,

I've recently started having pressure problems with my Vaillant Ecotec Pro 637 System boiler. When the system has been off for a while (and the water in the system has cooled) the pressure is often really low (certainly less than the min 1bar for the boiler to fire and often registering 0.0bar). When I add water to the system the pressure quickly goes up to the min required (about ~1bar) and then the boiler works normally. However, often, after it's been firing for a while, it can hit - or even exceed - its max pressure (3+ bar).

I assumed this was due to the expansion vessel. I did check and noticed that it had little pressure it in so pumped it back up to 1bar. That worked for a while but now, even that doesn't help.

I replaced the expansion vessel believing it was shot but it hasn't improved the situation. Same low pressure followed by rising pressure when boiler has fired for a whlie.

What may be interesting is that, when trying to purge the system, as soon as it starts firing (and the pump activates) the pressure instantly shoots up from 1.5bar to 2.1bar. Then - when the purging stops - it drops instally back down to 1.5 bar again. Problem with the pump or a blockage may be???

Hope someone can help here as I'm pulling my hair out and my plumber (who's been out 3 times) is pretty clueless on what is happening (suggesting it could be a multitude of things and therefore reluctant to try anyone thing that could fix it).

Thanks in advance,
J.

 

[EvilDrPorkChop]

Being the 637, does it just have the digital gauge or the manual one on the front also?

 

[JonWebb]

Being the 637, does it just have the digital gauge or the manual one on the front also?

Thanks for the quick reply. It has both a digital gauge plus a manual one inside the unit itself.

 

[EvilDrPorkChop]

And is the manual one correct reading with the digital one?

Have you made any system alterations recently, additional rads, changed radiators for different ones etc.

 

[JonWebb]

I'll double-check the pressure gauges; see if they're the same. No changes to the system though.

 

[EvilDrPorkChop]

I'll double-check the pressure gauges; see if they're the same. No changes to the system though.

The digital does generally overread, also they can be faulty as dirt can block them. Unfortunately you'd need to get your Heating engineer to replace the sensor if it is, as it involves removing the front of the boiler which on the Vaillants forms part of the case seal. So as a DIYer you cannot do.