How is air getting to my central heating pump

[FloppySock]

Hi all,

So since moving into this house my heating has been very tempremental in that the pump (grundfos alpha 2) seems to be getting airlocked all the time.

It's an old vented system with its own feed from the boiler going to the central heating pump (so no switching valve etc).

If I've not had my heating on for a day when I next fire it up the radiators don't get warm and then I look at the pump and even put the pump on the highest setting it's operating at 11w max and struggling to push the hot water around the pipes. The boiler then stops trying to heat the central heating and goes into a loop of firing up for 30 seconds then stopping.

The only way I get can it to fire up properly is if I then loosen the nut on the inlet pipe to the pump (blue in the pic) and let out a massive amount of air for 10 seconds or so, then if I put the pump on max it'll shoot up to 45w and all my radiators eventually become hot. The problem is if I turn the heating off for a few hours and fire it up again, the pump (or just before the pump) seems to be airlocked again? Then I have to follow the same procedure.

Not a problem right now whilst I have the floorboards up (pump is annoyingly in the centre of the back bedroom under the floors) but eventually I'll be redecorating and need to lay carpet etc.

So I'm wondering if anyone can help me diagnose how this air is continually getting into the system? Can try answer any questions to explain further if needed

Pic attached , thanks.

 

[polesapart]

Many possible answers here but a first check is

is your expansion tank (the smallest roof/loft tank) 1/3 full of water and if you press on the ballcock arm does water come through?

 

[Gasguru]

Boiler make and model and a diagram of the pipework needed.

 

[FloppySock]

Boiler make and model and a diagram of the pipework needed.

It's an old baxi solo 40/4 RS. Pipe feeds below:

Many possible answers here but a first check is

is your expansion tank (the smallest roof/loft tank) 1/3 full of water and if you press on the ballcock arm does water come through?

I'll check when I'm back in the house tomorrow. Both tanks are in the airing cupboard upstairs.

 

[FloppySock]

Many possible answers here but a first check is

is your expansion tank (the smallest roof/loft tank) 1/3 full of water and if you press on the ballcock arm does water come through?

Yes it's about a third full and when I push down on it water comes through to fill it back up. Pic attached - very awkward to get to as no room to get my big head above it.

 

[Gasguru]

Is the water level a couple of inches above the feed pipe outlet?
That vent pipe not dipping in the water?

 

[Lower]

Personally, whatever the problem is that is allowing air into the system, i'd get that pumped moved. Under a floor is a ridiculous place to put it.

 

[Gasguru]

The lot needs ripping out..gravity primaries were obsolete the day that boiler was installed...

 

[FloppySock]

Is the water level a couple of inches above the feed pipe outlet?
That vent pipe not dipping in the water?

Is the feed pipe outlet what I've circled here? If so the water level is a few inches above yes.

The vent pipe (big long slightly drooping one?) Isn't dipping into the water.

Personally, whatever the problem is that is allowing air into the system, i'd get that pumped moved. Under a floor is a ridiculous place to put it.

Yep you're right. Unfortunately during its lifetime this house has been subject to some questionable decision making along the way.

 

[FloppySock]

The lot needs ripping out..gravity primaries were obsolete the day that boiler was installed...

We'll be replacing the boiler with a combi at some point but it's a while away yet as funds are being spent making the house liveable & refurbing.

The rest of the water and piping system actually seems to be performing well, just the heating.

 

[Gasguru]

Sometimes these air problems are caused by blockages in the pipework/heat exchanger and the air can be pulled down the vent pipe.
As an initial quick idea cut the neck off a plastic coke bottle, fill it with water and tie it over the vent pipe so the pipe is dipping down to the bottom.
Mark the water level and then turn on the heating..see if it sucks the water down.

 

[picasso]

I would also try and turn the pump down at the front so it can vent.

 

[FloppySock]

Sometimes these air problems are caused by blockages in the pipework/heat exchanger and the air can be pulled down the vent pipe.
As an initial quick idea cut the neck off a plastic coke bottle, fill it with water and tie it over the vent pipe so the pipe is dipping down to the bottom.
Mark the water level and then turn on the heating..see if it sucks the water down.

I think you're getting somewhere - turned the heating on and off a few times, let the air out of the pump to get it revving away etc. Water level in the bottle has definitely dropped :

Before:

After:

Does this mean I need the central heating properly flushed out?

I would also try and turn the pump down at the front so it can vent.

Sorry thought you meant turn it around - do you mean turn the power down? Would leaving it on auto for a few hours help do you think? The instructions say putting it on the highest setting will help get air out.

 

[Gasguru]

It's only pulling the water down a little way...when it pulls all the water out you know you've got a real problem.

Try running the pump on fixed speed 1, that should be sufficient...I'm assuming you haven't got a microbore system (that's 8/10/12mm pipework).

Check all the connections from the pumped flow outlet on the boiler to the pump are tight especially the gland nut on the pump inlet valve and the large pump
inlet "nut"....this is where the system pressure is lowest and air is most likely to be drawn in.

 

[FloppySock]

It's only pulling the water down a little way...when it pulls all the water out you know you've got a real problem.

Try running the pump on fixed speed 1, that should be sufficient...I'm assuming you haven't got a microbore system (that's 8/10/12mm pipework).

Check all the connections from the pumped flow outlet on the boiler to the pump are tight especially the gland nut on the pump inlet valve and the large pump
inlet "nut"....this is where the system pressure is lowest and air is most likely to be drawn in.

That pic was from the first time I'd switched the heating on. After I posted I turned it on and off a few more times and it drew quite a bit more water out.

I've tightened each nut from the boiler to the pump inlet as much as I can and I left the heating on overnight on 'auto' which kept around 11-15w (max setting goes all the way to 45w) speed. I turned the heating off for an hour this morning and then started it up again and auto mode is struggling to get above 5w and max setting doesn't get past 11w which is what I normally see when it's airlocked.

Long shot but is there a possibility that the pump is on the wrong way around? - or would that see much bigger issues than an air lock every time it shuts off? We moved into this properly in March after the previous owner passed away so unfortunately have no info on the performance of the heating since we moved in.

Finally, I've been quoted £470 for a full system flush (there are 6 radiators in the property) - do I just bite the bullet and go ahead with this anyway?