cooler and erratic water temperature: relation to pressure

[Rod Hill]

I have a Viessman boiler that I noticed had been losing water pressure but relatively slowly (with no noticeable effects). After a while I topped up the pressure and it continued to work just fine. More recently I noticed the low water pressure and despite planning to increase it again, I went away for a week before doing so. This time however I've noticed that the water temperature for the shower, bath and kitchen sink whilst getting warm, then goes tepid/lukewarm before getting warm again and then cool again.

I was wondering are the two issues related and also what has happened that meant I now have erratic water teemperature that fluctuates between quite warm and lukewarm.

 

[ianmcd]

Unlikely to be related, there are lots of Viessmann boilers which one do you have

 

[Rod Hill]

Vitodens 100

 

[ianmcd]

I am guessing you are using it as a standard combi boiler and that you do not have a HW cylinder ? (can be installed both ways) if a standard combi, with the heating off and the pipes cool, run a hot tap and feel the flow and return pipes for the CH and see if either gets hot with the heating switched off, if they do you have a blocked plate heat exchanger or a faulty diverter valve

 

[Rod Hill]

Yes, a standard boiler. And yes, one of them does get hot so it sounds like those are the potential problems. Thank you so much for this advice! Are those relatively straightforward things to fix?

 

[ianmcd]

yes both faults are easily sorted, you wont necessarily have both faults probably just either one but both can cause the same symptom