Any ideas? Unreliable heating.

[garyevans]

How many rad? and is it a sealed or open vent system with a Feed&Expansion (small) Tank in the attic.
If a sealed system ensure that the system pressure is 1.5bar cold.
If a OV system, present setting of CC3 at 6.4M is too high IMO and can cause air ingress.
Suggest, in either case, c/o to constant pressure setting 2, CP2 which is 4.5M.
Press the setting button for ~ 3 secs until the yellow LED illuminates at the far right, then briefly press the button until the green LED and the yelloe LED next to it are also illuminated, you are now on CP2 at a constant 4.5M head.

(Also, these pumps have had more than their "fair" share of failures.)

I think it is an open vent system. I have no way of setting system pressure and I know there is a small tank in the attic. We have 5 rads upstairs and 7 downstairs. I will follow your instructions and see how we get on. Cheers.

 

[EvilDrPorkChop]

Pumps set too high and probably drawing air in, causing your downstairs circuit to air lock. The new Grunfos ones are more powerful than the old, you'll probably easily get away with I or II on the new model.

 

[garyevans]

Pumps set too high and probably drawing air in, causing your downstairs circuit to air lock. The new Grunfos ones are more powerful than the old, you'll probably easily get away with I or II on the new model.

Thank you. Lights now flashing like in screenshot on Constant pressure 2. Should I restart system to deal with airlock downstairs?

 

[EvilDrPorkChop]

Thank you. Lights now flashing like in screenshot on Constant pressure 2. Should I restart system to deal with airlock downstairs?View attachment 79951

Bleed any rads. Turn HW on, on it's own. Let it circulate round the HW system. When Hot and returning, turn HW off and CH on. Let upstairs rads get hot, when they're hot turn them all off and it should force it through to downstairs.

See how you go on 2, if it keeps airlocking you may need to turn it down to 1.

 

[John.g]

When you have done the above go up to the attic and get someone to stop the boiler and watch and see if any spurt of water from the vent when the pump stops probably a few minutes after switching off the boiler, then get them to restart the boiler/pump and watch again for any pump over.

 

[garyevans]

Bleed any rads. Turn HW on, on it's own. Let it circulate round the HW system. When Hot and returning, turn HW off and CH on. Let upstairs rads get hot, when they're hot turn them all off and it should force it through to downstairs.

See how you go on 2, if it keeps airlocking you may need to turn it down to 1.

Thanks to both of you. Issue now sorted. You have been a massive help!!!

 

[John.g]

Glad you are sorted.
Some OV systems with the traditional V,C,P system still have problems with air ingress with a pump head > than say 3.5/4.0M that may be required for systems with a large number of rads or small bore piping can be "cured" by changing the above to a combined vent and cold feed like my 50 year old system (from new), I could run my system with one rad and still get no carry over at a pump head of 6M.

 

[garyevans]

Glad you are sorted.
Some OV systems with the traditional V,C,P system still have problems with air ingress with a pump head > than say 3.5/4.0M that may be required for systems with a large number of rads or small bore piping can be "cured" by changing the above to a combined vent and cold feed like my 50 year old system (from new), I could run my system with one rad and still get no carry over at a pump head of 6M.

Cheers. I am no plumber so much if that is like a different language. Sadly, it seems that as predicted CP2 might still be too much. Good heat last night, this morning but this evening after about 3 hours, I could hear a different 'tone' in the pump and once again the downstairs rads went cold. Trying to change to CP1 and go through same steps as last night. Bloody nightmare.

 

[John.g]

Its quite likely that you have a partial blockage where the cold feed joins the system, if you still have a problem at CP1 @ 3M then almost a certainty IMO. Any idea of the old pump (and setting).

 

[garyevans]

Its quite likely that you have a partial blockage where the cold feed joins the system, if you still have a problem at CP1 @ 3M then almost a certainty IMO. Any idea of the old pump (and setting).

This was the old pump. Was mostly on second speed but more recently 3.