Grant Vortex Condensing Combi 26 hot water problems

19 Feb 2018
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United Kingdom
Hi all

I have a problem with my Grant Vortex condensing combi 26 oil boiler.

When I run the hot water for a bath after a few minutes the water runs luke warm, turn off the hot tap and wait 5 minutes and it is hot again. It’s not even getting hot enough, to run a full bath. When we moved into the property 4 years ago it never seemed to be a problem and over last few months. Also have noticed that am having to top the boiler up about every six weeks with water to re presure. It is due a service once I located a good engineer as last one we used has stopped turning up. It would be good to have some ideas as to what it could be before the engineer comes or even thing I could try myself first.

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Temp failure is normally either dhw plate exchanger blocked or the blending valve or both.
Thanks for the reply’s is there anything I can try myself first to see if it helps / improves
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Run your hot tap and feel the flow pipe from the DHW ht exch. If it is very hot, but the outlet from the mixing valve is cool, then the mixing valve is the probable culprit. If the outlet from the ht Exch is not too hot, then the Ht Exch is probably scaled up. Compare the heat from the dhw flow pipe to the primary flow through the ht exch. If the primary flow is too hot to touch, then you can rule out the thermistor. If the return from the ht exch is as hot as the flow, then scaling is probably your problem.
Try reducing the flow of water to see if that helps. It may take longer to run a bath but at least it will be hot.
Don't offer too much advice to the guy you have called out. He will see you as a smart **** and probably not come back either.
HI All

Apologies for the delay I've felt the mixing valve and the hot which I've marked as H is hot to touch (cant leave finger on for more than a couple of seconds) about the outlet is no where near as hot to touch


So I'm guessing this could be the issue. so a likely starting point

Not sure which pump I would check is running through, and not sure where theeese bits are ''Compare the heat from the dhw flow pipe to the primary flow through the ht exch'' sorry not very technical.

Would never dream of offering any advise to the engineer, would just like a rough idea of what it could be. I guess I just need to source a good one now to come out


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Mixing valves are available on line for around £70 and are easy enough to change. Just remember to isolate the cold supply, and protect the pumps and burner from any spillage. You can usually get away with re-using the original nuts and olives which makes the job easier. You also need to slacken off the connection from the DHW ht exchanger to give you room to manoeuvre the valves.

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