Potterson boiler keeps cutting out after a few minutes

[mattbroad]

Hi, this is my first post so please bear with me :-)

I have a potterson conventional boiler in my kitchen (downstairs) and a hot water cylinder in the airing cupboard in an upstairs bedroom. I have a control panel that sets when the h/w and c/h comes on. I have a grundfos selectric 15/50 pump, also in the airing cupboard. Recently this pump started making a loud whiring/vibrating noise (a bit like the noise made by Dr Who's tardis) when the hot water came on at 6:30am ready for baths etc. The boiler still worked, the h/w and c/h still worked but this noise was too much to take each morning.

I turned the pump up to 3 (was on 1) to see if this would fix it but made it worse. I assumed, not being a plumber in any way, that it could be air stuck in the pipes so I drained one of the upstairs radiators to see if this would fix the problem. Needless to say it made it worse!! Now when the h/w or c/h (or both) come on the boiler starts, the pump starts but after a few minutes the boiler starts making a noise like it is boiling which increases and then it cuts out (i assume this is to stop it over heating much like a kettle). The pump in the airing cupboard continues to work (i assume as i can feel it vibrating and changing the speed makes it faster/slower) but the pipes above and below it don't get hot.

Any suggestions would be very welcome before I call an engineer which could cost an arm and a leg, and how could I enjoy my nice warm house with only one arm and one leg?!?

[hicks]

I'm not a plumber or heating engineer, but when we recently had boiler problems (cutting out), it was caused by a failing water pump. We replaced the pump, and everything was back to normal.

[mattbroad]

Hi thanks for the reply. Can you remember if the pump was still making any noise as if it was working fine?

[hicks]

Well in fact the opposite. On close inspection of the pump there was a distinct lack of noise, and the casing was blisteringly hot. It was pretty clear that it wasn't functioning correctly.

[mattbroad]

My pump seems to be working, as much as I can hear it turning, but the hot water does not seem to leave the boiler causing it to heat up until it reaches the maximum tempratue causing it to trip out.

Could it be air stuck in the pipes preventing the pump from distributing the heated water from the boiler?

[hicks]

I'd still put my money on your pump failing though, if it's making strange whirring/grinding noises, as you said in your first post. Doesn't sound healthy does it?

[mattbroad]

True but the noise did go away after a while until I bled the radiator and now it does not make the whiring noise but the water is not taken from the boiler either.

arggh I wish I were a plumber then I'd know what to do :0)

[The Natural Philosopher]

Hit the pump take off the screw in the middle and try and free the pump by rotating the spindle. Replace the pump.

[mattbroad]

will the pump leak any water when i remove the screw?

[marvelus]

How did you drain a radiator?

There is probably an airlock tween the boiler and the valves. Vent out all the gas on each radiator with the radiator key. There maybe a vent near the valves aswell and also the screw on the side of the pump needs venting as NP said.

With the original problem I think you need to do a chemical flush. It fixed my noisy pump and made the radiators warm again!

[mattbroad]

Hi Thanks for the reply.

I unscrewed the vent on the top left of the radiator which released little trickle of water for a couple of minutes.

you mention btween the bolier and the valves. What valves? (sorry for sounding stupid)

[marvelus]

Cant see how that can make it worse. If the water was black/brown your system needs a flush.

Its a bit of plumbing with a motor on it. The motor is a metal box and has a wire going fromit to a junction box. Likely near the cylinder.

Normaly the hot water comes from the boiler to the pump and then to the valves.

You should be able to feel the progress of the heat from the boiler to the pump .

[marcusb3495]

i am an heating engineer--from what you have said sounds like you have a blocked cold feed-very common this time of year--i have had 4 this week which means you have not enough water in system if you take your big screw out of the pump and see no water dripping then it proberly going to be your cold feed blocked--(if the pump is in the airing cupboard) also when the screw is out you be able to see or feel the pump running just gentily poke a screwdriver in there --if theres no noise then its your pump

a good tip ,,put your heating on occasionally in the summer --just for minutes becuase it doesnt half help--so many people leave it off for

6months then expect that it going to work--if you didnt start your car for 6months would u expect it to start?

[mattbroad]

Hi thanks for the reply. How would i go abouit unblock in the cold feed? I have opened the big screw (very nerve racking didn't know if I was going to get showered with water!) and no water came out. I can turn the motor and have turned the hot water on whilst the screw was removed and can see the motor turning.

[Ed Sirett]

Go into the loft and give the float valve some exercise. Chances are that it has stuck in the shut position and the water has evaporated away.

Hopefully this is the problem then you come down and bleed the air out of the radiators and hopefully all should be well when you turn on. Later bleed the air out again when the hating is off.

[mattbroad]

[mattbroad]

have checked the float valve and it seems fine the tank is full of water. I have tried bleeding all the radiators but the upstairs ones do not seem to have any water in them.

[Ed Sirett]

OK. Chances are that there is a crud plug just where the feed pipe joins the main circuit.

Shut off header tank and bail/syphon the water out if it. Cut into the feed pipe in a suitable straight section that gives you access to the crud-plug location (catching dregs as needed). Break up crud-plug. Reconnect feed pipe using push fit or compression. Refill and bleed as needed.

[mattbroad]

for the great advise Ed. Im not the worlds best DIY, can I ask how much I should expect to pay for a quilified person to do this? Thanks

[Ed Sirett]

How long is a piece of string? £100? Including finding out the problem an then fully fixing it.