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Plumberpro, Home Appliance Technician
Category: Appliance
Satisfied Customers: 634
Experience:  Heating and hot water heating appliances experienced
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Glow worm swift flow 75 Boiler works ok water heating

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Glow worm swift flow 75
Boiler works ok for hot water heating but when central heating is switched on water pressure rises to venting point.
Hi is it going above 3 bar and dumping out of the safety valve?
Customer: replied 2 years ago.


Hi , most likely the expansion vessel is flat and needs recharging( can be done with a foot pump) . thus vessel takes up the expanded water when it is heated . if it is flat it gives the water non option but to overessurise and dump out of the safety valve.
Release the pressure to zero by draining water into a pot from a radiator bleed valve.
Take cover off boiler .
Find the expansion vessel(round metal circular case with a cap to recharge )
Take cap off . push the pin in and make sure water doesn't come out ( if it does replace the vessel)
Pump up to 1.5 bar, replace cap .
Refill boiler to 1.2 bar.
If you have a big heating system ,is over 10 rads you may need an additional vessel
Customer: replied 2 years ago.

Thanks for that. I believe you are right because this has happened previously. I can find a brass

object with a red plastic cap on. Is this what I am looking for? I can't find anything that looks like the images on the internet ie a red circular casing!

If this is what I need how do you get the cap off?

Its not always a red casing . the capis like a car tyre cap, .
I think it's at the back and the cap may be at the top rear of the boiler . but make sure the power is off before feeling around up there as sometimes there's a live air pressure switch at the back
Customer: replied 2 years ago.

Thanks for your response. Found it recharged it as instructed. Hot water still ok. Central heating on pressure climbs rapidly to vent still?

Thanks for your help any further suggestions welcome.

I wonder if the pump is faulty. Do you know how to test the pump . in the middle of the pump face is a small , disc . undo this and put a screwdriver inside,you should feel the rotor spinning . there may be some water drips out, so you may need and olkd towel underneath. If the pump is red hot this would indicate a faulty pump too
Customer: replied 2 years ago.

Thank you. A plumber has just been and confirmed your diagnosis. The pump is knackered. A pump is for sale on e bay for 57.00.

He says its not worth it and is quoting for a new boiler. Is it such a big job to replace a pump? How much should it cost for labour? You will already have a positive feedback thanks again for your help.

No , its an easy job to replace the pump , get rid of that guy or tell him you just want the pump changed . but ii t should only be a couple of hours Max to change.
However , how old is the boiler? Might be worth considering a new one , but get at least three quotes and get a recommendation from friends and neighbours etc.
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