Shower temperature help please.

[WilburSki]

Hello,thank you for the previous assistance.

Our shower mixer is supplying hot then cold then hot then cold water,we had a new Mira sequential shower mixer fitted in the summer in lieu of a working but externally corroded and filthy mixer valve (same for same).
The temperature fault is new yesterday,having looked through the many shower threads here gave us some ideas on what to look for.

The combi boiler is a baxi 105ee (not instant) think it's been here 15 years,we are new here.

Watching the boiler when running a hot tap,it fires into action running up to 60 degrees the boiler stops burning gas.The water runs cold for 1 minute then fires up then cycles hot cold hot cold.

The boiler is not maintaining hot water temperature. It does the same when running heating fires up then off then reignite continuous cycling.

The boiler does not overheat or need resets.

Any advice is very welcome,thanks in advance.

 

[Madrab]

Get someone in to service the boiler, if it is reaching cutoff temp on hot water demand then it could be a restricted HE, or a faulty stat.

The Ch behavior could just be it's reaching the set temp on the return, again though get an engineer to service and test the HW/CH functions to diagnose any issues..

 

[ericmark]

I am not a plumber, however have had the same problem, I had to find a shower head which would allow more water to flow, and always use it flat out, never throttle it back, could be build up of lime in the shower head.

 

[WilburSki]

Thanks for the help.
The boiler was serviced just before the shower temperature started playing up,the gas service company has been back and fitted a new plate water exchanger.

Still no improvement and have been informed a full system power flush has to be carried out or a new boiler fitted.Not what we want to hear.

Has anyone got any ideas on a repair ? The new shower valve mixer has also been exchanged by the plumber that fitted it,the plumber does not do gas.

Any help greatly appreciated.thank you.

 

[dilalio]

If there is an issue with hot water from all hot taps then the problem is at the boiler or hot feed from it. If the plate hex was changed and you are again getting problems then there are either other faults within the boiler or debris from the rest of the system is making its way into the plate hex and reblocking it so some kind of flush is required... or a new boiler!
You could try a DIY drain and flush of the CH circuit and rads.
Plenty of resources explaining how to do it.

 

[MeldrewsMate]

If it cycles the burner on-off-on-off when running a hot tap then you can see the problem isn't related to the shower, old or new. You say the burner cycling occurs on the heating cycle too; this clearly points towards a lack of flow in your boiler's main heat exchanger. You will probably benefit greatly from a flush of the whole system. If you can do a simple draindown and flush that should help, and may well improve things enough for the boiler output temperature to become stable. Failing that a full system powerflush may be required - but make sure the powerflushing device is connected in place of the boiler's internal pump or you won't flush the secondary heat exchanger loop - the one that provides domestic hot water.