Baxi 105 hot water problem

[Alfie25]

A relative has a baxi 105 combi which is suddenly taking a long time for HW to reach the taps. I haven't visited myself but apparently the radiators are also getting warm when only HW is called. Is this most likely to be a diverter valve? Would anything else cause these symptoms on this model of combi?

The 105's power controls allow the following 3 options:
OFF
ON - CH/HW
ON - HW only

Like most domestic installations I imagine, it's normally set to ON -CH/HW permanently, however to help diagnose this problem my relative set the control to ON - HW only, and when in this setting, the HW comes through as quickly as it always did. Is this control a manual/mechanical mechanism? My thinking is if the diverter valve was stuck, then turning the control to ON - HW only wouldn't make a difference, but here it is. As soon as it's turned back to ON - CH/HW, the radiators heat up when HW is called and HW takes a long time to come through.

 

[Agile]

That is purely an electrical switch.

That is a common fault caused by a faulty diverter valve if it is a plain 105 ! But that would not respond as you have described!

But its much more likely to be an "instant" version with a more complex fault.

Tony

 

[Alfie25]

Hi Tony. It's a 105HE (not instant version), about 10 years old and serviced annually.

 

[Agile]

If it really is not an instant then the operation you have described is not logical!

 

[Alfie25]

Maybe what I wrote wasn't clear so I'll try and clarify. NB. at no point is any heating being demanded.

Control knob set to CH/HW - when hot tap is opened, radiators start to warm up and hot water takes ages to come through (approx 4 minutes).

Control knob set to HW only - when hot tap is opened, hot water comes through as quick as it always did (30 seconds or so). Radiators are not heating up.

I presume if the radiators heated up when the control knob was set to HW only then we could be certain the diverter valve was to blame, but as it isn't, then what's happening is illogical?!

As an aside, why does this model have the control knob for different CH/HW and HW only options? A combi can only do one at a time so why not a simple on off switch?!

 

[DP]

You have three options. OFF being one
HW being second where boiler gets powered up and sits like that until a hot tap is run. Now boiler runs to heat cold water passing through it on the way to the tap that is running

Third position is HW/CH where the clock/ timer/ thermostat etc circuit is brought into play

In HW position, CH side is deactivated
In HW/CH position hot water delivery is exactly the same as in HW position of the selector

 

[Agile]

In most 105HE models, the diverter valve is hydraulically actuated by the DHW flow. Just like the non HE models were.

There MIGHT be a later version with a motor driven diverter valve! Although I must say I have never seen one!

Tony

 

[Alfie25]

In most 105HE models, the diverter valve is hydraulically actuated by the DHW flow. Just like the non HE models were.

There MIGHT be a later version with a motor driven diverter valve! Although I must say I have never seen one!

Tony

Tony, if you haven't seen it, it probably doesn't exist! So are we still none the wiser to this particular boilers symptoms? Could the diverter valve not be only partially kaputt?! Whatever it is, turning the control knob does make a difference. The problem is only apparent when it's on CH/HW. Ah well, we'll have to get an engineer in, but I was hoping to get a handle on what was up prior.

 

[AGAS]

A relative has a baxi 105 combi which is suddenly taking a long time for HW to reach the taps. I haven't visited myself but apparently the radiators are also getting warm when only HW is called. Is this most likely to be a diverter valve? Would anything else cause these symptoms on this model of combi?

The 105's power controls allow the following 3 options:
OFF
ON - CH/HW
ON - HW only

Like most domestic installations I imagine, it's normally set to ON -CH/HW permanently, however to help diagnose this problem my relative set the control to ON - HW only, and when in this setting, the HW comes through as quickly as it always did. Is this control a manual/mechanical mechanism? My thinking is if the diverter valve was stuck, then turning the control to ON - HW only wouldn't make a difference, but here it is. As soon as it's turned back to ON - CH/HW, the radiators heat up when HW is called and HW takes a long time to come through.

I've read it three times and I'm still confused , or is it me ??

 

[Agile]

I am not confused.

But if it is the standard diverter at the left side, then the alleged behaviour is not logical.

 

[AGAS]

its a case of standing in front of the boiler yourself TBH , i know he may be trying to help but MAY have confused the matter and probably a straight forward fix . going by what he is saying there can be three different scenario issues i can imagine happening ( not all at once of course ) but depends which model he has ,
keep us informed with what happens ALFIE .

 

[Agile]

It would help us if you were able to remove the front cover and take a photo of the lower half of the boiler insides and post it up here!

Tony