Baxi 105e Instant - Slow Heating???

jd_hants · 24 Nov 2007

On CH demand, boiler fires up, pump runs, gradually heats up, reaches max temp (80 deg led) in about 30 seconds, flame extinguishes and pump continues to run until temp decreases to 30 deg led before the boiler fires up again?

Result is that the rads get hot but not too hot to touch. Problem is that they dont seem to radiate enough heat to actually raise the temp of the rooms to much more than 19/20 degrees. This is despite TRVs being on max.

Have checked all rads and they didnt need bleeding. Boiler pressure constant at about 1.5-2 bar. DHW demand / instant DHW demand all seems to work properly (i.e. switching on/off when needed and returning to CH mode afterwards).

I have about 13 rads in all. If I switch off some of them then YES some of remaining ones are too hot to touch.

Wondered whether the pump isnt up to the job??? It was replaced during the summer - its the same as the original but has the words "Low Energy" on it. Do you think this pump is not beefÿ enough??? Or maybe the entire boiler is just not capable of heating so many rads??? Maybe I need to replace it with something with a higher central heating system capacity???

Would appreciate anyones thoughts on the matter.

Many thanks

baxpoti · 24 Nov 2007

It's getting up to 80° too quick.

Start with checking the return filter is not blocked.

jd_hants · 24 Nov 2007

Just for information : just had another look at boiler. When the temp reduces down to 40 led, the pump contines to run for about 3 minutes or so before the boiler fires up again!

I guess a better question would have been:

What is the criteria for the flame being extinguished in CH mode. CH demand is still active (i.e. room stat set higher than room temp) and boiler temp set to maximum.

(do you think it may be overheating because the pump cant shift enough heated water???). Just a guess!

Thanks again

jd_hants · 24 Nov 2007

Thanks for the reply. That sounds logical as I had noticed that the return is always only warm to the touch.

Will go and check.

jd_hants · 24 Nov 2007

OK - return filter bit black but clear.

Timed whole process:

Pump starts, boiler fires up

Temp rises to 80 degrees from 40 in about 25 seconds

Remains at the temp for further 30 seconds - sounds like it is still heating the water up as pump gets bit noisier - sounds like its either pumping loads of aerated water or its actually boiling!!!!

Flame extinguishes but pump continues

Gradually cools down to 40 in about a further 30 seconds

Continues to run at 40 for a further 1 minute before repeating again

Have just turned all the rad lockvalves to fully open to see whether boiler will remain on for longer if it can pump the heated water away easier.

jd_hants · 24 Nov 2007

Boiler does seem to stay on longer before 'tripping???'. I think I mustbe on the limit or exceeded the 80 litre maximum capacity.

Is there a heftier pump I could upgrade to or is it the entire boiler which I would have to replace to upgrade to, say, a 100 litre capacity system??

baxpoti · 24 Nov 2007

How hot is the flow pipe? Measured at least 1m away from boiler

namsag · 24 Nov 2007

Could it not be the divertor partialy sticking and just sending the water around the boiler with slight amount going to heating

baxpoti · 24 Nov 2007

namsag said:
Could it not be the divertor partialy sticking and just sending the water around the boiler with slight amount going to heating

Patience old man!

jd_hants · 24 Nov 2007

OK - opening each of the lockshields "seems" to allow the boiler to run for a bit longer before the flame extinguishes. Trouble is now my farthest rad doesnt get so hot any more.

anyone know what the difference between the Grundfos 15-60 (original pump) and 15-60 Low Energy (replacement) is. Just wondered if is runs
slower or something. Cant find any spec on it on Grundfos site.

CH flow temp is approx 55degrees. Bit confused why boiler 80 degree light comes on if temp is only 55??? Although thermometer is just one of those pipe thermometers and might not be that accurate?

I read another thread earlier which refers to the strange bubbling noise coming from the pump as kettling??? Thats exactly what it sounds like. The hot water isnt being pumped away quick enough?!?!

jd_hants · 24 Nov 2007

ok thanks - How do I check the divertor valve???

jollyjingle · 27 Feb 2008

jd_hants said:
On CH demand, boiler fires up, pump runs, gradually heats up, reaches max temp (80 deg led) in about 30 seconds, flame extinguishes and pump continues to run until temp decreases to 30 deg led before the boiler fires up again?

Result is that the rads get hot but not too hot to touch. Problem is that they dont seem to radiate enough heat to actually raise the temp of the rooms to much more than 19/20 degrees. This is despite TRVs being on max.

Have checked all rads and they didnt need bleeding. Boiler pressure constant at about 1.5-2 bar. DHW demand / instant DHW demand all seems to work properly (i.e. switching on/off when needed and returning to CH mode afterwards).

I have about 13 rads in all. If I switch off some of them then YES some of remaining ones are too hot to touch.

Wondered whether the pump isnt up to the job??? It was replaced during the summer - its the same as the original but has the words "Low Energy" on it. Do you think this pump is not beefÿ enough??? Or maybe the entire boiler is just not capable of heating so many rads??? Maybe I need to replace it with something with a higher central heating system capacity???

Would appreciate anyones thoughts on the matter.

Many thanks

water not getting getting away from heat exchanger ,prob pump fault

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Baxi 105e Instant - Slow Heating???

namsag

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