Combi boiler issue or Shower?

[pete23]

Hi
Yesterday my shower in the bathroom started to run cold. It started fine but then ran cold...then got warm again before running cold again. This continued and then just ran cold. Other taps ran hot as usual so thought it could be the shower/cartridge. Instead of fiddling with manufacturers etc I went and bought a middle of the road new shower (thermostatic bar) and fitted. Then tested and seemed okay. Showered this morning and similar problem...though not as frequently. Whilst the wife showered I watched the combi boiler. It fired up when hot water was called, it ran for about a minute and then stopped. About a minute later it fired up again for hot water again. This then continued. As said, all the other hot taps call for demand and the boiler fires up and stays fired up until I turn the tap off. Boiler is a Baxi Platinum 28HE. Pressure is good (between 1 and 1.5 bar cold)
Any ideas??

 

[king of pipes]

Partially blocked plate heat exchanger is the most likely culprit you will need a GSI to sort it out its a easy fix . Kop

 

[pete23]

Thanks for your advice KOP, would this only affect the shower

Partially blocked plate heat exchanger is the most likely culprit you will need a GSI to sort it out its a easy fix . Kop

Thanks for the advice KOP, would this only affect the shower? Not doubting your vast knowledge but why only the shower? As mentioned, the other hot taps work fine with the boiler?? Anyway, will try and get an engineer out. Thanks again, Pete.

 

[moonlight]

Did you replace the non return valves in your shower? assuming there were some. Might be cold passing back through shower valve.

 

[king of pipes]

It's quite possible as you are restricting the amount of hotwater being used when mixing the shower supplies, if the plate heat can't absorb and exchange the heat being produced by the boiler then it will reach its highest temperature and shut down , you can simulate the fault at a hotwater tap by partially closing it, my advice is get the boiler drained the plate heat exchanger removed and throughly cleaned it can then replaced, I power flush them through with a pressure washer it's amazing how much debris can accumulate in there . Regards kop

 

[John.g]

I think on this model that once the flow switch sees a flow > 2 LPM that you will get hot water, as suggested above maybe worth throttling in a hot tap until heating stops and then measure it to get the actual minimum flow rate.

 

[pete23]

Thanks very much for all the comments they have been very helpful. I will try and get an engineer out....if someone will visit? Thanks again. Pete.