Open vented system, No HW or CH, BAXI 80HE boiler shows Ignition Lockout after tried to start a few times

[Johntheo5]

Yes I did look into F&E cistern and it is fine - no sludge build up (I drained the system down in June and cleared all the sludge that was there and there was a fair bit of that).

The sludge might have been depositied elsewhere as well but w'll see.

Yes I did look into F&E cistern and it is fine - no sludge build up (I drained the system down in June and cleared all the sludge that was there and there was a fair bit of that).

I am not sure how long it takes to reheat the cylinder as I did not have to use HW for a while after it went cold last time.

I will take the flow/return readings next time I am up there.

With venting air from it am I risking anything (obviously with the boiler etc turned off)? I just do not want to create any more problems for myself

Don't bother with that venting, the AAV will get rid of it eventually or the thumbvent until its installed.

The flow/return readings should tell something.

Did you notice if the valve that you checked full open was in the coil return only and wasn't a by pass betwwen the coil flow & return, can be checked the next time anyhow.

 

[fandyman]

Re the coil again and the valve you said you checked fully open, is this valve on the coil outlet only, ie its not a by pass between the coil flow & return?.

Are you referring to the gate valve here? It is few meters away from the coil and is on the cold feed pipe. I believe this valve is to isolate the tank F&E tank from the system for maintenance and is not directly related to the coil outlet AFAIK and is not a by pass neither.

The sludge might have been depositied elsewhere as well but w'll see.

Don't bother with that venting, the AAV will get rid of it eventually or the thumbvent until its installed.

The flow/return readings should tell something.

Did you notice if the valve that you checked full open was in the coil return only and wasn't a by pass betwwen the coil flow & return, can be checked the next time anyhow.

Still to do the flow and return reading tomorrow.

 

[Johntheo5]

Not that valve. This valve is sometimes installed on the coil outlet and can be throttled to balance the flows between the HW coil and the CH circuit, more rarely, a manual bypass valve with a bit of pipework is sometimes installed between the coil inlet & outlet.

 

[fandyman]

Not that valve. This valve is sometimes installed on the coil outlet and can be throttled to balance the flows between the HW coil and the CH circuit, more rarely, a manual bypass valve with a bit of pipework is sometimes installed between the coil inlet & outlet.

Ah ok I get you. There is no such valve and no bypass valve.

 

[fandyman]

Ok checked the readings and inlet pipe has about 35C-40C and the outlet pipe has 45C-50C.

 

[Johntheo5]

Say a 10C dT, a bit unusual but the flow may be into the bottom (normal outlet) of the coil and out through the top (normal inlet), that gives a coil output of, 10*60*10/860, 6.98kw, (assuming flowrate @ 10LPM), fairly low, and may account for the boiler having difficulty in getting away and it will certainly cause the boiler to cycle sice the boiler's minimum output is > than the coil output. Change the pump to CP2 and note the pump power and the coil dT after a few minutes.
Did the boiler fire up OK on HW only and run for at least a few minutes? Are you still venting air from the thumb vent?

The boiler will never cut out if its flow temp is only 45C/50C and the cylinder stat is set higher at say 60C but if the boiler is cycling continuously then that would account for the average low coil inlet temp.

 

[fandyman]

Say a 10C dT, a bit unusual but the flow may be into the bottom (normal outlet) of the coil and out through the top (normal inlet), that gives a coil output of, 10*60*10/860, 6.98kw, (assuming flowrate @ 10LPM), fairly low, and may account for the boiler having difficulty in getting away and it will certainly cause the boiler to cycle sice the boiler's minimum output is > than the coil output. Change the pump to CP2 and note the pump power and the coil dT after a few minutes.
Did the boiler fire up OK on HW only and run for at least a few minutes? Are you still venting air from the thumb vent?

The boiler will never cut out if its flow temp is only 45C/50C and the cylinder stat is set higher at say 60C but if the boiler is cycling continuously then that would account for the average low coil inlet temp.

Ok I will change to CP2 and report back on the pump power and coild dT. The boiler fires up on HW only for few minutes only (that's the last time I checked yesterday). Yes I am still venting the thumb vent from time to time and some air comes out every time but not much.

I suppose the constant manual bleeding of air from thumb vent is one of the telltales of the boiler cycling correct or could it be the sludge? On the other hand the flow rate shows almost correctly on CC2 which is confusing. I will check the flow rate on CP2 + temp reading and report back.

 

[Johntheo5]

The boiler cycling should have no effect on the flowrate.
You might just check that the boiler flowtemp is reaching 60/65C or whatever you think it should by running the CH or the CH&HW to get it to fire continuously for awhile and then measure the boiler flowtemp.
You may be generating hydrogen due to sludge build up, you can test for that by holding a glass over the vent and holding a match to see if it lights, or something like that.

 

[fandyman]

How do I check the boiler flowtemp is reaching 60/65C? Do you mean take off the casing and measure the flow and return pipes with infrared thermometer?

 

[Johntheo5]

The pipes must be visible soon after leaving the boiler, if not just put on the HW&CH and measure at the coil again, but preferrably clse to the boiler.

 

[fandyman]

I changed today to CP2 and for CH & HW the pump is showing 35W. The coil dT was about 10C - similar to how it was before. I did not do the HW only test yet. Will do tomorrow.

I am still to check the boiler flow and return pipes. They will be visible above the boiler so should not be a problem.

One thing I noticed is when I change pump speed and bleed the thumbvent there is always some air escaping before water flows. Wonder where could the air be getting in to the system and can only think of radiators which a rusty and leak from time to time. There has not been any inhibitor topped up for a while now.

 

[Johntheo5]

I changed today to CP2 and for CH & HW the pump is showing 35W. The coil dT was about 10C - similar to how it was before. I did not do the HW only test yet. Will do tomorrow.

Were the coil temps similar to last time? "inlet pipe has about 35C-40C and the outlet pipe has 45C-50C."

You will have to test that "air" for hydrogen.

 

[fandyman]

So looking at your table this 35 W for CH+HW in CP2 is way too low I suppose? Should be 45W so significant drop.

 

[Johntheo5]

That was specific to one installation, your 35W on CP2 gives a flowrate of 0.8m3/hr,13.3LPM, I get that (with a spotlessely clean system) at a 3.6M head so would expect 14.9LPM at 4.5M (CP2) so not hugely different. I also notice on mine that there is very little difference in flowrates between CH&HW & HW only.

 

[Johntheo5]

Took a few readings off my daughter's basic 95L (30"X18") cylinder late last night, gas fired boiler, SP 70C, minimum output, 5.0kw.
From a cold cylinder at 20C to 45C. the boiler fired continuously, the flowtemp then began to rise and the burner tripped at 75C when the cylinder reached 50C, it continued to cycle until the cylinder reached its SP of 60C. When the boiler flowtemp began to rise meant that the boiler was running at 5.0kw so coil absorbing 5.0kw, the coil dT was 5.5C which gives a circ flowrate of 13.0LPM, this from a system (Vokera Vision 20S) boiler which would probably be running with a pump head of ~ 6M.