Greenstar 24i junior warm water

[gasbusters]

Hello

I was hoping a boiler repair man could advise. I've recently qualified as a gas man, about 8 months back and am starting to venture into boiler repairs.

I've got a Greenstar 24i junior which was working ok a few weeks ago but now only gives lukewarm water.

I've descaled the DHW heat exchanger but still the same problem.

When the hot water is running, the boiler is fired up and the flame stays on, but its not giving hot water. I was advised to buy a new heat exchanger which I have done but i've not yet fit it as I dont want to risk losing £90 if the fault could be something else. Could someone please advise if there is any other component that could be faulty?

The U-Gauge is showing the working pressure at the meter at 21.5mb when the hot water is running

I had a similar issue with a Heatline Vizo which was resolved by descaling the heat exchanger, but unfortunately on the Greenstar thats not worked.

Any advice would be much appreciated. I've re-registered for the gas chamber section as I lost my previous login details.

 

[Cgas]

You should post in the combustion chamber for more help. Does flow get hot when hot tap is running ?
Edit; just reread your post about CC.

 

[gasbusters]

Hello Cgas

Do you mean the hot water flow out the boiler? That gets warm but wont get hot. The central heating though works perfectly fine though.

 

[picasso]

Make sure the cold supply isi t passing into the hot supply, been to a few boilers with new PCB,s, plate heate exchangers, thermistors ect to find its a passing tap or shower.

 

[picasso]

I think cgas means does the flow to the central heating g get hot when running a tap?

 

[gasbusters]

Make sure the cold supply isi t passing into the hot supply, been to a few boilers with new PCB,s, plate heate exchangers, thermistors ect to find its a passing tap or shower.

Oh ok this is interesting that you have raised this. I turned off the house mains. Drained boiler. Also turned off the isolater of cold water feed to boiler. Took off the heat exchanger. Turned on the house mains to flush the heat exchanger in bathroom and water started pouring out the boiler as if water was still going into the boiler. Water was also flowing out the hot water tap in the bathroom even though the cold feed to boiler was isolated, and the heat exchanger had been removed from the boiler.

I did a gas safety here about 8 weeks ago and everything was working fine. Tenant says problem only started about 2 weeks ago. No plumbing work has been done since the gas cert was issued so not sure what is happening!

Just to add, the thermostatic shower does not get hot, UNLESS you turn on the cold water on the basin! Its a bizzare scenario. In fact I dont understand why/how the tenant discovered that turning the cold tap on the basin allows the water to get hot on the shower.

 

[picasso]

Showers have cheapo non return valves which have a tendancy to stick open, when the hot nrv sticks open there is nothing to stop the cold from passing into the hot supply.

 

[gasbusters]

fantastic! so you would advise to isolate the mixer shower? the only other mixer they have is a kitchen mixer tap

 

[picasso]

Yea isolate the shower, if that sorts the problem stick a nrv on the hot pipework to the shower valve.

 

[gasbusters]

wow just wow! you were spot on Picasso! i had an old shower valve in van so put that on, tried hot water and bingo! hot water working perfect! Cannot believe it was something so simple! I honestly would never have even thought of the shower. I wonder how many boiler men must waste time and effort and money on similar faults.

Thank you once again Picasso.

 

[picasso]

No problem.