Baxi 105 HE - DHW and potentially diverter issues?

Hi,
I am having issues with my Baxi 105 HE (not the Instant model). There are two issues which may be related and hoping someone can advise on what this might be. I've read plenty of other threads for 'similar' issues which tend to point to the diverter potentially failing or requiring new diaphragm's in either the diverter or the DHW flow valve but none seem to fot the bill exactly here and doesn't make sense to me based on some of the tests I have done. Issues are...

1. DHW fluctuates in temperature in our upstairs bathroom and is most evident when using the shower

a) The boiler is located in our kitchen. Whenever using the hot tap in the kitchen, the boiler works fine and the water is constantly hot. Boiler fires up as expected and burns constantly until the DHW demand stops
b) Not the case upstairs for either our bathroom taps (less of a prob) or our thermostatic shower. Taps are usually hot all the time but can go cold sometimes. Shower no longer goes very hot and regularly has intermittent cycles of cold temperature. Flow of the shower itself doesn't appear to be that bad.. (certainly not much less than it used to be when was working ok). When looking at the boiler this weekend whilst the shower was on, the boiler would fire up, the burner burning towards maximum, then it would slowly reduce (i.e. the height of the flames physically getting smaller) until they eventually go out. This isn't the case for the downstairs tap which will slowly reduce but then maintain a minimal flame controlling the temperature.

2. The Central Heating works fine on its own and appears to fire up ok and warms all of the rads as expected. If the heating is on when there is a demand for DHW (from either upstairs or downstairs), as soon as the DHW demand stops, the heating seems to struggle. It will then keep igniting and resetting itself every few minutes. Will do this for anything up to 5-10 mins or so before eventually staying on. Throughout this process, the burner light will come on when the boiler ignites for around 5-6 seconds, then there seems to be the start of an increasing "whoosh" noise suggesting its increasing the gas to meet the demand but then that trips and the burner goes out. Process then repeats until the CH will eventually come back on.


So far, I've seen that both the upstairs/downstairs DHW demands will flick the DHW pressure switch at the front so that the burner ignites. This is the case for both the DHW pressure switch and also the one on the diverter at the back (which the manual says is the CH pressure switch but pretty sure was pushing switch on DHW demand also - is this right?).

Any help/confirmation anyone can give would be appreciated. If there are any tests I could do to at least get some indication of what the issue is before ordering parts that would also be very useful.


Thanks,
Jon

Repairing boilers is not just a matter of changing parts ( unless you work for British Gas ).

Its a task of carefully diagnosing the faults and doing whatever is necessary,

Your plate HE may be blocked.

The gas valve may well need adjusting. CORGI job !

The gas valve may even be intermittent. CORGI job !

The ignition and flame sensors may be out of adjustment or just need optimising. CORGI job !

The PCB may be intermittently failing.

There are so many possibilities and to decide what they are in your case will require tests and measurements !

Tony

Thanks for the quick response and agree that its not just a case of having someone tell me what parts, then I order, the I fit (esp. if its gas related)

I'm simply looking for some advice at this stage if someone has suffered similar issues so I get an understanding of it before deciding best course of action.


With regards to some of your suggestions about the HE exchange plate being blocked or the gas valve's needing adjusting, etc - the only reason why I wouldn't think it was related to these is because running DHW downstairs is without issue (and for the most part the tap upstairs - just not the shower) which would suggest it was more flow-related as the system operates normally in all but a few cases.

Also, its not what I'd call intermittent. Its not like for eg, the central heating won't fire again after a DWH demand sometimes... its all the time - regular as clockwork. If I start the CH from cold - thats fine everytime also.


Not sure if this helps but thanks for the feedback anyway.

Agile said:

Your plate HE may be blocked.

The gas valve may well need adjusting. CORGI job !

Click to expand...

I'd put money on these two.

Just so I'm clear - do you think this is the case for issue 1) or 2)... or even both?

start by checking the dhx heat exchanger... order some washers first for it, just to make sure you can put it back without drama. the dhw hex would be sus if you can find black 'grit' filling /blocking the plates inside. someone will be along to suggest a good chem for removing the sludge. if it does have that junk in it, it would be a good idea ton have a magnaclean installed and possily you may need the system cleansing.

It's the non return valve in the hot supply to the shower,just cut another in line if acessible.

No 2 is a CORGI's job!

Hi guys. Thanks for all the advice here!

I've finally had a chance to look through these suggestions today and here's what I've found...


Firstly, ridiculous error on my part which I noticed whilst looking for the secondary heat exchanger this morning!! I don't actually have the 105 HE is seems - just the 105e - apologies for that. Guess suggestions may change after this...


I took a look at the DWH heat exchanger this morn. Took it out and had a good look around it after draining the primary circuit. Not a whole lot there to be honest... most of the water drained was sludge/limscale free and water seemed to be flowing through the heat exchanger ok suggesting no blockages, etc...


I did a couple of checks on the shower too this morning. Isolated the cold mains to the shower just to see how much hot was coming through. Flow rate was descent (8 l/min) and water was both a) scalding when I first tried and 2) warm at best when I second tried a bit later

During the second attempt, the boiler was only lighting the temp to 60 - 70 whereas the first (and when I use the downstairs tap) usually takes this to the full 80.

Checking on this occassion.. the burner was no longer "fading" out per se - just cutting out. Lit the 70, cut out, cooled down and repeated. Never really got the burner on for more than a min before just cutting out.

I also checked the DHW temp sensor this morn and it looked limescale, etc free and tested its resistance and all seemed good there too...


Do you think this could still be a gas valve issue or does anything else spring to mind given my erronous boiler type statement earlier on... I'm on the verge of having to get someone out anyway at this point I think unless its something obvious...

Thanks again for the help...

Jon

Agile said:

Its a task of carefully diagnosing the faults and doing whatever is necessary,

Your plate HE may be blocked.

The gas valve may well need adjusting. CORGI job !

The gas valve may even be intermittent. CORGI job !

The ignition and flame sensors may be out of adjustment or just need optimising. CORGI job !

The PCB may be intermittently failing.

There are so many possibilities and to decide what they are in your case will require tests and measurements !

Tony

Click to expand...

You have not done the simple test of turning off the cold water into your boiler and seeing if any water comes out of your hot taps!

Have you tried just turning DOWN the temperature control on the boiler DHW ?

Tony

not true! I did it just neglected to mention it sorry...

I isolated the mains feed into the boiler itself. Opening the hot taps throughout the house reveals no water at all. not downstairs or up.

opening the shower does still produce water though given thats its a thermostatic a mixer shower (I'm assuming thats expected as the cold comes from the mains direct)


I haven't tried turning the temperature down any but will try that.

a question I have thats raised from all this however is.. even if I have the temperature turned up to max, should I expect all of the temperature lights to switch on all t heway to 80 deg. given that I read in the manual states that DHW is only heated to 65 (pretty sure I read that). that seems to be were it is stopping with the upstairs taps when it goes throug hits hot/cold issues (yet downstairs goes all the way to 80 so there's still a prob either way

The lights only measure the system water in the boiler.

On DHW that should not go so high unless the plate heat exchanger is blocked or not transferring the heat properly.

Those lights are only a guide and any fault finding relies on proper temperature measurements inside the boiler.

Tony

had an interesting find on this one.

had a corgi friend over this afternoon and when he took t hecovers off inc inner door panel - couldn't understand why everything seemed to work ok and I couldn't get the boiler to cut out on either CH or DHW.

putting the inner door panel back on, the problem came straight back. this was tested again by simply unscrewing the inner door panel to allow some some more air in during which everything worked as expected. pushing it shut, within a few seconds, the burner would extinguish. not necessarily the safest practice but proved the point.

this is the inner door pannel in between the outer door panel and the combustion chamber panel just for clarity.

so, at this point, a quick test off the flue for blockages revealed nothing and the air pressure switch was briefly tested (blowing/sucking to cause the switch to operate). getting two fairly cheap parts (air pressure switch and flame sensor electrode) which could be suspect to see if this solves...

will know in a few days and report back...

anyone seen this before? am hoping given that it seems reproducable that its not going to be the pcb now which is a relief or the gas valve. saw some old posts with similar probs but no real resolution that seems to fit this case...

Jon

If he was really CORGI registered to work on gas boilers then something is wrong as he should be able to immediately recognise whats wrong.

Are you sure that he is not just registered to change gas meters or perhaps gas pipes in the street?

Tony