Vokera Linea 28 DHW Problem

[Brett Jackson]

Just recently my boiler has started to exhibit a problem whereby the DHW takes longer than usual to reach full heat, and the full heat isn't really that hot (49-50 C). When the tap is turned off the temperature reading on the boiler jumps up a bit, maybe by 10 C or more.

The problem only seems evident when the CH is not running. It also seems to vary slightly, in that the temperature seems to fluctuate slightly during a shower.

The DHW temperature control on the boiler seems to have no effect - and never has done even from new. Resetting the boiler has no effect. There are no error codes etc. The only other problem I have with the boiler is that occasionally in the winter (maybe 3-4 times per year), and strangely generally around late afternoon/early evening the boiler fails to ignite - I kind of put this down rightly or wrongly to gas pressure issues.

From a previous post there was mention of the diverter valve being a possible cause, but the CH flow pipe doesn't seem to get particularly hot unless the water is running for a while (e.g. a for a shower).

Thanks in advance Brett

[Ed Sirett]

What flow rate are you getting in litre/min from the hot tap? At this time of year the boiler needs to heat the water by 45C

So the 8-9 litres/min should be the max you should get. If it's somewhat less then there may be a fault in the modulator. If it's about 8-9 litres/min then you will need to draw water a little less quickly to get it hotter.

[Brett Jackson]

Since posting I've done a little more investigation...

I removed the head from the diverter valve and pushed the valve in manually. The water seemed to reach full temperature as expected. I also checked the voltages in to the diverter head and although I've no knowledge of the exact signals required, there was definate switching of 240 volts when switching between CH and DHW. The only thing that concerned me was that there was a fair bit of force req'd to manually operate the valve. Not sure if this is normal or not?

The flow rate hasn't changed from when the boiler was working normally, and when I say 49-50 C that's just the readout on the boiler - the temperature from the tap is maybe only 40C or so.

I'm thinking that this is now either a fault with the diverter head, or with the mechanical valve itself being too stiff.

Thanks Brett

[Ed Sirett]

But that part of the story doesn't entirely sit with the CH pipes not getting hot when running the HW.