Baxi 105e burner problem.

[molegrip]

Sounds as if it is partially blocked/restricted, hence the poor initial flow through the system.

Thanks, yep it was horribly gunged up with all sorts - matted. I got it cleaned up and replaced everything including a rigid filling loop, and that was the start of hours of confused faffing about, as the boiler would not re-fill through the loop at all. I took the loop off again, filter out, couldn't see anything amiss and was pretty stumped. Hours later...removed the loop to test in the sink and it seemed dodgy, ie not passing a flow of tap-water. I made up a bodged arrangement of garden hose, a length of 15mm copper pipe, jubilee clip and a flexible hose to fit to the CH return valve, all connected to the outdoor tap, and only a gentle flow got water going into the boiler and re-pressurizing it with ease. So the loop is definitely knackered and will be replaced. Onwards and upwards....

 

[DP]

What is a rigid filling loop.
Where in the filling loop does one find a filter?
Filling loop is fitted between cold water pipe and normally the return pipe
On the 105 it can be located, as an option, on the return and cold-in valve by using a dedicated Baxi kit which had a flexible link that is removable and only connected for purpose of filling up.

Genuinely intrigued by above.

I can understand a lay person may not have correct terminology, equally responding to questions from professionals can resolve issues.
A professional meanwhile needs to act responsibly as an enduser may or may not be up to the task of carrying out a repair that could lead to expensive damage or injury. Case in point is Forum rule prohibiting gas advice on open forum

I reiterate, Baxi 105e is a tame pussy cat, easy to fix in hands of someone who knows its workings. It can also throw up Wobblies that will be well beyond capabilities of many, sometimes even plumbers who do not do repair work.

 

[molegrip]

Sounds as if it is partially blocked/restricted, hence the poor initial flow through the system.

Back again. I cleaned out the Return pipe filter, and have fitted a new external expansion tank (old one almost just full of water). It has a 'new' (re-con) complete diverter. Everything looks good to go, no leaks, 1 Bar pressure etc. BUT....keeping temper....the CH is still failing: it starts no problem, using the old style timer clock as the On switch, which i've done for years, but after shooting up to 80C on the front panel in a couple of minutes, the burner stops, flame dies. Looking at the CH diverter chamber, the actuating pin stays fully UP and thus the microswitch fully on. If i just leave it running with the flame off, the flame will re-ignite, but again only until the temperature reaches 80C, and then the burner shuts off again. The pump stays on and is not noisy at all. Any ideas welcomed with open arms!

 

[Johntheo5]

Can you hear the boiler modulating down after it fires up?, the burner will normally cut out if/when the flow temperature reaches SP+5C, is there a manual or auto bypass valve installed?.

 

[molegrip]

Can you hear the boiler modulating down after it fires up?, the burner will normally cut out if/when the flow temperature reaches SP+5C, is there a manual or auto bypass valve installed?.

Thanks for that. I went through a number of ever-hopeful procedures, checked all electrical connections including on the PCB, and did find surface rust on the main Earth tab on the chassis (just to the left of the DHW diaphragm), so cleaned that up. Checked the fan and the venturi, close looking at everything really. The hot water has never been a problem, so while leaving the CH still running (but the burner gone off) i ran the hot water tap again for a minute, and then when shutting that off, the CH came back on and for some reason the burner stayed on - long enough for me to go around the system starting to balance the rads. Long enough to reach 80C on the panel. Very odd, and not having a definitive answer to the problem i'm not relaxed about it as yet. It might be just a matter of the system getting fully purged and settled down after all the work done recently, don't know. Work done: complete new diverter assembly; removal and cleaning of Return pipe filter; replacement of old external expansion vessel with new one - this seems to have cured the pressure - swing i've had for a long time, reducing the swing from as much as 1.5 Bar (so from 1 Bar to 2.5 Bar), to a more acceptable 0.5 Bar. Thanks again. Hoping to get through one more Winter with a true antique - no not the missus!

 

[Johntheo5]

The minimum output of that boiler is 11kw to CH so if your radiator demand is < this the burner will cut out eventually at SP+5C, if the rad demand is equal to or > 11kw then it only requires a flow rate of 7.9LPM, 474 litres/hr, to keep the boiler dT at 20C which means that the rad/boiler return temp would need to be 60C to cause a burner cut out at 80C, your circ pump head should be 3.6M at this flowrate which should be quite adequate for most systems. so maybe check your installed rad output and the next time you get it running, you shouldn't be able to hold the boiler return (60C) when the flow temp reaches 80C, the only other reason that I can think of to cause a very high return temperature is that either a manual by pass is full open somewhere or a ABV, if installed is set far too low or is jammed open, of course a faulty circ pump will give similar symptoms but this could give a low return temp with a very high boiler dT and still trip at a flow temp 80C.

 

[DP]

The minimum output of that boiler is 11kw to CH so if your radiator demand is < this the burner will cut out eventually at SP+5C, if the rad demand is equal to or > 11kw then it only requires a flow rate of 7.9LPM, 474 litres/hr, to keep the boiler dT at 20C which means that the rad/boiler return temp would need to be 60C to cause a burner cut out at 80C, your circ pump head should be 3.6M at this flowrate which should be quite adequate for most systems. so maybe check your installed rad output and the next time you get it running, you shouldn't be able to hold the boiler return (60C) when the flow temp reaches 80C, the only other reason that I can think of to cause a very high return temperature is that either a manual by pass is full open somewhere or a ABV, if installed is set far too low or is jammed open, of course a faulty circ pump will give similar symptoms but this could give a low return temp with a very high boiler dT and still trip at a flow temp 80C.

Regardless of return temperature, if the flow temperature Rise is rapid, the OH stat will disconnect the gas valve supply, ie modulation will not take place. Look up scenario where P2P is blocked up and hot water delivered is erratic.

Burner is shutting down in this case, anticycling delay is initiated which is terminated when hot tap is run.

Your final thought fits

My money is on diverter associated components. For positive diagnostics I would be using clamps to take temperature readings to locate lack of flow to radiators.

 

[kidgreen61]

Could either the flow/return iso valve be in the shut position, even though it appears open?
You clearly have a lack of circulation.

 

[Johntheo5]

Or, obviously could be restriction in system and boiler Hx due to sludge build up, there may be some indication of this 4 years ago.

"Baxi 105e 'Fault on Pump or Low Pressure' error."​

 

[Harry Bloomfield]

You clearly have a lack of circulation.

Exactly, as I suggested in post 14 above.

 

[DP]

Exactly, as I suggested in post 14 above.

OP is only looking at posts that agree with his thinking.

Lack of circulation can of course be the pump but then flow manifold would not let the burner come on- this component is fairly well balanced that would show up poor pump operation or air in the system
Could be plumbing beyond the boiler
Not the main heat exchanger as there would be HW issues too otherwise
Diverter too as have resolved similar issue previously.

OP has not said what boiler he has as two options work very differently

 

[molegrip]

Hi all, thanks to all recent contributors. The good news from late yesterday continued this morning, with the boiler running steadily and reaching 80C at a normal pace and without any burner failure. The clean-out of the filter in the CH Return valve must have helped as it was seriously clogged. The diverter replacement also must be an improvement, and the new expansion vessel is restricting the increase in pressure bewteen cold and hot to just 0.5 Bar which i haven't seen for a few years. One supplementary issue - the hot water filter in the pump manifold - Baxi manual calls it a 'cartridge' - i have tried but have never managed to loosen the shallow-headed bolt to get at the filter. So it's not been touched for at least 5 years. The access around the back of the gas inlet pipe is cramped to say the least, and the size of the bolt head fits a 15/16ths imperial socket but there's no room for a bar. What does get this bolt to move ? Apart from the access problem, it's so tight that it bears the scars of mole-grip teeth dug into the brass from way back.

 

[Johntheo5]

What temperature is the boiler flow temperature set at?.

 

[molegrip]

What temperature is the boiler flow temperature set at?.

Hi, the antique pre-condensing Baxi 105e only has the simplest dial with no actual numbers on it. I have been running it on Maximum during this period of repairs so the panel lights have hit the 80C mark. Weirdly the system has never had any kind of thermostat, neither room stat or TRVs. I might make a room stat the next job. For reasons of economy i'm not planning to run it with th flow temperature set at Maximum if i can get all rads up to hot at a lower setting than that.

 

[ianmcd]

For reasons of economy i'm not planning to run it with th flow temperature set at Maximum

With the amount you have spent on parts you didnt need you could run it on max all winter and still have saved money