Baxi 105e water temperature and flow issue?

[TheAndrew]

Hi,

I have a 2-3 year old Baxi 105e combi boiler running central heating and heating the water. For a couple of months now, I've noticed that my bathroom shower is not maintaining an even temperature, alternating between running hot and cold every 20 - 30 secs or so.

Separately, I've also noticed that, when I turn on the hot tap in the bathroom sink, with a moderate flow, from cold, the flow reduces to a trickle as the boiler seems to start up. If I increase the flow a little, it reduces itself again, and eventually comes out slowly but very hot. When I open the tap more fully, everything seems to settle down to normal temperatures.

My heating engineer took a cursory look last week and suggested a new thermostat in the Mira Excel shower would cure that part and that the tap issue was nothing to worry about. So I fitted a new thermostat cartridge in the Mira yesterday (£90 ish) and it hasn't made the slightest difference...! I'm now concerned that the rest of the "nothing to worry about" advice may have been dodgy... and I still need to sort out the shower temperature proble.

I'm in Cheltenham - aparently hard water..? Could it be that the problems are caused by the 105e furring up somewhere or maybe a thermostat or pump or some other flow problem within it? I changed the diaphragm about a year ago and it worked fine after that. The fitting doesn't appear to be leaking. Grateful for any other thoughts or advice.

regards,

Andrew

 

[corgiman]

Sounds to me like the domestic hot water heat exchangers is starting to scale up badly.

probably need to change it and get a decent in line scale inhibiter fitted

 

[TheAndrew]

Hi,

Many thanks for this advice. It is kinda the way I was thinking - but in a non-technical way. Your diagnosis sounds like the reason for the problems and your solution sounds like it would solve them.

I'll make sure there is an in-line scale inhibitor this time. Great advice, many thanks

Andrew

 

[Agile]

Most modern boilers control the temperature adequately to prevent lime scale even in Bracknell. ( Worcesters excepted )

I would expect the problem will be rusty debris in the primary side of the secondary heat exchanger. Clean or change it and consider treating the system if its very dirty.

Tony

 

[TheAndrew]

Thanks,

Sounds like basically the same area for the cause - a restriction in the flow exchanger area. I'll mention all these to the corgi man.

many thanks for your help

Andrew

 

[corgiman]

Agile

sludge up primaries would explain the temp fluctuations but would that really explain the loss of pressure at the hot tap?

I know that the makers set the temp as to stop the scaling up of the plate to plate heat exchanger but I regularly come across scaled up ones from all the main makers.

 

[Agile]

Real lime scale will only occur if the temperature control has failed.

This will sometimes happen if there is a fault with the NTCs.

It will also occur if the primary is blocked and thus the flow through the primary is reduced. Thats a "fault" condition though. The "fault" of the installer who did not power flush!!!

Having said that I have virtually never seen a scaled up secondary plate HE. Some Worcester boilers seem to have a serious design fault as I have seen several badly limescaled in London where the water is not that hard compared with Bracknell or Reading.

Tony

 

[corgiman]

I removed a DHW heat exchanger from an isar on friday,it hadnt got a combi mate fitted, and it was chokka with scale.

Good point on the NTC's though Cheers mate