Main 24 HE hot water issue

[curlyj]

Hi guys,

I've been using the site for info for some time now so first off, thanks for everything you might have posted which has helped me any many others already.

I've looked at so many answers in respect of the current problem I have and still no joy. I've rung the helpline, who've basically told me what I suspected already and still I'm getting nowhere so this might be a fruitless request/question.

Boiler is a Main 24 HE, I've swapped PCB, gas valve, thermistor, checked diaphragm and every other aspect of hot water side, including plate heat exchanger, all appears as it should be.

Pressure at burner goes to low gas when running hot tap pretty much straight away, which would suggest a blockage of some kind, all other things considered, but I can't find a thing.

If I run the water at around 3 or 4 liters/min I get a temp rise somewhere near to what I would expect and the burner will stay lit, no failures of any kind.

So, basically I'm stumped. The saving grace for me is that it's my own boiler so I don't look like an idiot in a customers house.

Thanks in advance.

 

[gasafengineer]

Pressure at burner goes to low gas when running hot tap pretty much straight away, which would suggest a blockage of some kind
.

Obviously you are a RGI bearing in mind the parts already replaced , seems you have missed carrying out a few simple checks with regard to 'blockage of some kind' , to which i asume refers to gas pressure/rate

 

[dcawkwell]

What does it do in central heating mode?

 

[picasso]

What voltage are you getting on the modulator coil when you run the hot water on full flow ? (should be between 1 and 9vdc)

 

[Agile]

I think that should be about 18v on full flow.

If you are an RGI then you should post in the CC and we can give you full advice on gas settings etc.

Tony

 

[picasso]

I think that should be about 18v on full flow.

View media item 35547
saves guessing.

 

[curlyj]

I am gas safe registered.

Central heating runs fine, or did when it was last used, it's been a couple of weeks since I did any checks so can't remember all I've done to be honest but gas pressures are as they should be, I'll check modulator voltage as soon as I can but I'm sure it checked out ok when I last had a go with it.

Been busy with hols etc so it's been left in abayance and up to press has only been an issue for washing up water. It's been puished to the back of my list of jobs of late but I'll get back to it asap.

Cheers so far though guys.

 

[adlplumbing]

join cc and post ur gas safe reg number and give quick call
p.s. have treid baxi tech

 

[curlyj]

Pressure at burner goes to low gas when running hot tap pretty much straight away, which would suggest a blockage of some kind
.

Obviously you are a RGI bearing in mind the parts already replaced , seems you have missed carrying out a few simple checks with regard to 'blockage of some kind' , to which i asume refers to gas pressure/rate

Regards a blockage, it was what I was assuming, in respect of the heating circuit and especially plate heat exchanger, which was pretty much what I was told on ringing the help line, but having checked every component, I can't find a problem anywhere.

Gas side, all is fine, just modulating down to low gas after 20 seconds or so, but anything that might cause that has alresady been switched out for new or repalcemnet parts as I have access to a working boiler to check, never been so baffled.

 

[curlyj]

join cc and post ur gas safe reg number and give quick call
p.s. have treid baxi tech

I have spoken to baxi, I'll get onto cc as soon as I have a chance, bit busy at the mo so may have to be tomorrow.

Cheers

 

[adlplumbing]

have you checked with temputure difrential between flow and returns to secondary heat exchanger

 

[curlyj]

have you checked with temputure difrential between flow and returns to secondary heat exchanger

I have yes, As the heating is running fine, I would expect if there was a problem with either main or secondary heat exchanger or anywhere else on the heating circuit I'd have noticed it when the heating was calling.

Think I'll check on the modulating coil voltage again as there seems to be an issue with the boiler dropping to low gas, but I know the gaas valve and the pcb are both good so it shouldn't really be that.

As I say, bit lost, I'm sure I'll find it eventually.

 

[adlplumbing]

did you do this with hot water running f&R from secondary heat ex
if temputer too low going in then pcb
if right and starts to creep up the heat ex is sludged
if correct check diaverta not passing

 

[curlyj]

did you do this with hot water running f&R from secondary heat ex
if temputer too low going in then pcb
if right and starts to creep up the heat ex is sludged
if correct check diaverta not passing

Already swapped pcb and flushed and checked heat exchanger, diveter valve also appears to function as it should, striped and checked, also striped and checked inlet/return manifold.

I'm stuck for time to do anything with it right now, which is more of a problem than the problem itself, I will have to make time as soon as...

 

[Agile]

I am gas safe registered.

Cheers so far though guys.

We have guessed that you are registered. However thats not the point.

This site rules are that we do not give any advice on gas or safety aspects that could encourage DIYer to try gas work which he may not be qualified or experienced for.

The CC is specifically for G-S engineers where we can give advice on gas related matters where its only going to be seen by registered people.

Whilst most are short of work you seem to be lucky enough to be very busy ( or you work for one of those social maintenance contractors where you are pushed too hard! )

Tony