Boiler cuts off after 2 minutes

mark71

I had drained central heating system, replaced a radiator and refilled the system. I bled radiators (started downstairs) and checked automatic air vents. Now after firing the boiler it runs for about 2 minutes and then cuts off.

My system is fed from a water tank in the attic and I have a cylinder in hotpress. The boiler (Ideal Classic) is downstairs with a pump (Grundfos UPS 15-50x18) and an expansion vessel on top of the boiler. There is no pressure gauge, just a pressure relief valve and an automatics air vent beside the vessel. Also, there isn't a connection for refilling the system from the water supply - I refilled the system from the water tank in attic.

I assume (perhaps wrongly) that the boiler cuts off because there is no flow in the system. Could it be caused by an airlock in the pump, or could a dirt be blocking the pump? Did I miss anything else?

Any suggestions?

ntpm

mark71 wrote: »

I had drained central heating system, replaced a radiator and Ttrefilled the system. I bled radiators (started downstairs) and checked automatic air vents. Now after firing the boiler it runs for about 2 minutes and then cuts off.

My system is fed from a water tank in the attic and I have a cylinder in hotpress. The boiler (Ideal Classic) is downstairs with a pump (Grundfos UPS 15-50x18) and an expansion vessel on top of the boiler. There is no pressure gauge, just a pressure relief valve and an automatics air vent beside the vessel. Also, there isn't a connection for refilling the system from the water supply - I refilled the system from the water tank in attic.

I assume (perhaps wrongly) that the boiler cuts off because there is no flow in the system. Could it be caused by an airlock in the pump, or could a dirt be blocking the pump? Did I miss anything else?

Any suggestions?

You seemed to have done things ok.
I dont understand if you have a sealed system then you should normally be refilling from a mains cold feed (for higher pressure) via a filling loop, gauge and pressure reducer/regulator.
Or do you have an open vented system that MUST be fed from the small f&e tank NOT the large domestic cold water tank

Sounds like air lock in pump... Did you open the bleed valve on pump.
Could be airlocked in boiler. Should have automatic air vent at boiler if not crack fitting at boiler to check for air.....let boiler cool down first.

sullzz

As said above it sounds like the pump is airlocked or jammed , when pump is running remove the large screw in the front of the pump , you should get a small trickle of water , then insert a flat head screwdriver into where the screw came out if you can't feel it spinning try turning it with the screwdriver , also check that the small cap on the top of your auto airvent is open to let the air out of the system

mark71

ntpm wrote: »

You seemed to have done things ok.
I dont understand if you have a sealed system then you should normally be refilling from a mains cold feed (for higher pressure) via a filling loop, gauge and pressure reducer/regulator.
Or do you have an open vented system that MUST be fed from the small f&e tank NOT the large domestic cold water tank

Sounds like air lock in pump... Did you open the bleed valve on pump.
Could be airlocked in boiler. Should have automatic air vent at boiler if not crack fitting at boiler to check for air.....let boiler cool down first.

I would expect a filling hose as well, but there isn't any. I think plumbers refer to this system as semi-sealed.

The system is fed from a small dedicated tank, not from the large domestic cold water tank.

You may be right about airlock in the pump. I would have tried to bleed the pump, but there is not easy access to it (see picture). The pump is installed very close to the ceiling with the bleeding screw facing the ceiling. The automatic air vent is at boiler as well and it seems to be working fine

mark71

sullzz wrote: »

As said above it sounds like the pump is airlocked or jammed , when pump is running remove the large screw in the front of the pump , you should get a small trickle of water , then insert a flat head screwdriver into where the screw came out if you can't feel it spinning try turning it with the screwdriver , also check that the small cap on the top of your auto airvent is open to let the air out of the system

Thanks sullzz. Your suggestion makes sense, now I have to figure out how to get to that screw.

slavetothegrind

nasty installation there, you will need a stubby flathead for the pump. even then the pipe may be blocking access.
the black plastic dust cap on the vent in the picture is defo loose?

mark71

slavetothegrind wrote: »

the black plastic dust cap on the vent in the picture is defo loose?

Yes, the cap is loose.

ntpm

Some plumbers need shooting...how are you supposed to vent the pump let alone replace it. The position and orientation of pump seems a perfect position for airlocks...
As stated by slavetothegrind use a dummpy screw driver or a coin and pliers. Be cereful the screw only has a couple of threads.

sullzz

If you had someone to help you , you could lift the vessel out of there as it's on a flexible pipe , it should be just clipped to the boiler at the back , if it was me I would slightly loosen the nuts on the pump valves on the copper sides , not the pump side , I would not reccomend trying to close the pump valves as 98% of the time these leak , then rotate the pump so you can service it , I'd only do this if you cant get access to the screw with a stubby screwdriver or if the pipe is in the way

mark71

How big job it would be for a plumber to actually fix the installation so that the pump becomes accessible and serviceable?

I am sure I will need to drain the system in the future, so it may make a sense to move the pump now.

kscobie

Now thats rough:)

sullzz

mark71 wrote: »

How big job it would be for a plumber to actually fix the installation so that the pump becomes accessible and serviceable?

I am sure I will need to drain the system in the future, so it may make a sense to move the pump now.

You could relocate the expansion vessel to your hotpress and just turn the pump , only a couple of hours work

mick987

You will have to turn the pump so that the motor is level with the pipework, or the motor will burn out.

mark71

Guys, thanks for all your suggestions.

I've managed to bleed the pump. I turned the large screw about a half turn, got a bit of water out and then turned the screw back. However, the boiler still cuts off.

Previously the pump was relatively noisy after the boiler cuts off. After bleeding the pump, it is now very quiet. Not sure whether this is a good news - hopefully the pump didn't stop working all together .

Any other suggestion? Could the boiler be air-locked?

Buford T Justice

When the boiler cuts out, does it trip the high limit stat?

mark71

Fingers McGee wrote: »

When the boiler cuts out, does it trip the high limit stat?

I think so. Once the boiler is switched on (I do it by manually increasing the target temperature on the room thermostat) it runs for about 2 minutes and then cuts off. At that point whatever I do I cannot fire the boiler again and have to wait until it cools down. Pressing the overheat thermostat button on side of the control panel doesn't make any difference.

Once the boiler is cool, I am able to fire it again.

Buford T Justice

High limit stat would need to be manually reset

slavetothegrind

circulation problem methinks, you really need to sort that pump install out so you can determine if the pump is actually running, i suspect not.

Billy Bunting

mark71 wrote: »

Guys, thanks for all your suggestions.

I've managed to bleed the pump. I turned the large screw about a half turn, got a bit of water out and then turned the screw back. However, the boiler still cuts off.

Previously the pump was relatively noisy after the boiler cuts off. After bleeding the pump, it is now very quiet. Not sure whether this is a good news - hopefully the pump didn't stop working all together .

Any other suggestion? Could the boiler be air-locked?

You have bled it but you didnt/couldn't check if the pump is actually running it sounds as if not, allow it to cool, remove the large screw from the centre of the pump again, this time insert a screwdriver to ingage with the top of the pump shaft and manually turn the shaft a few times, replace screw and try running system again.

kenmason

Certainly sounds like you got an air lock which may or not be around the pump - much more likely to be within a bit of pipework running horizontally. Again it sounds as if cooler water is not returning to the boiler which is being turned off by its internal thermostat not the roomstat. Depending on how your system is wired it may be possible to run your pump without actually firing the boiler. It doesn't matter too much but but if you can do this it cuts out the noise of the boiler firing and also the slight possibilty of damaging the boiler.

What I do in these circumstances is to turn off the valves on all radiators except a radiator upstairs closest to the boiler then run the pump. It may be that without having to pump water through all the radiators it has enough grunt to shift the airlock. If the pump has more than one speed, switch it up to a faster speed which will increase the grunt through the pipes. As you do this listen to the pump and it should give you noises that will indicate whether water is passing through the pump. If you do not hear watery wooshing noises switch off again.

Occasionally I have to resort to draining down again and refilling much more slowly which often seems to reduce to amount of air that gets trapped in the system then run the pump on fast to push it through to somewhere it can vent, usually a radiator.

Hope this helps!

sanbrafyffe

a plumbers worst nightmare is an airlock.

noise in the boiler is referred as kettling i think.#

god that installation is a mess

do as ken said.well written

mark71

It turned out that the pump wasn't in the best shape, and the draining and refilling pushed it over the edge. It has been replaced now, and everything works fine. Thanks for your help.

RAFA B

Our heating went the other evening. Noticed the rad in the room was hot at the top and cold at the bottom. Checked the switch in the kitchen and it was still on. Turned it off and switched it back on and it came on outside at the boiler for around 4 minutes but didn't kick in like it normally does and then cut out. Tried it again the next morning and same again. Checked and there seems to be enough oil in the tank because got caught before. Had it serviced last April and was told the boiler was working great so hopefully nothing major wrong. The fella is calling over to have a look tomorrow.

jimf

RAFA B wrote: »

Our heating went the other evening. Noticed the rad in the room was hot at the top and cold at the bottom. Checked the switch in the kitchen and it was still on. Turned it off and switched it back on and it came on outside at the boiler for around 4 minutes but didn't kick in like it normally does and then cut out. Tried it again the next morning and same again. Checked and there seems to be enough oil in the tank because got caught before. Had it serviced last April and was told the boiler was working great so hopefully nothing major wrong. The fella is calling over to have a look tomorrow.

this passed unseen by all I would think

did you get it sorted

RAFA B

jimf wrote: »

this passed unseen by all I would think

did you get it sorted

Yes got sorted there an hour back. Needed a new pump. All back working thankfully.