Glow worm Swift Flow 75 combi boiler problem

[Shabs]

Inside my boiler is a Grundfos switch with a dial for numbers 1/2/3. the boiler works fine when this is on 1 but if i switch it to 2 or 3 (which i assume will make the water hotter) the boiler will not turn off if i run the central heating. it just constantly stays on burning. However if i turn off the downstairs radiators it goes back to it's stop-start usual self. The problem also is that the water does not get any warmer with the switch at 2 or 3.

Does this dial control the water temperature? or any clues as to how i would sort it out... many thanks guys

[Ed Sirett]

Almost always you set a combi boiler's internal pump to 3 (unless the instruction say otherwise). Sometimes the instructions say that you may turn it down but will have reduced water heating performance - which on most installations would not be welcome.

This setting is how hard the the pump works.

To make the radiators hotter try the knob on the outside of the boiler!

[Shabs]

OK I agree that the pump should be set to 3, but if i move the switch into position 3 I can hear a sort of different noise, but when I start the central heating from position 3, the boiler does not turn off, just runs continuous and the pressure goes sky high. With the pump on no. 1 the boiler does the stop-start stuff. How would i get the pump onto no.3 but the boiler doing the usual stop-start routine.

[Ed Sirett]

It is very unlikely that setting the pump to the high setting will by itself cause any problem. You should now procede to tackle the cause of the high pressure directly. See the Sealed system FAQ it is likely that as the _average_ water temperature rises the system pressure is rising too quickly. The cause for this is likely a failed expansion vessel.

The boiler will likely operate correctly once the water temperature has stabilised but this may mean the prsssure will go even higher and water is thrown out of the vent pipe.

[JohnB]

Very very useful FAQ

My sealed system seems to have partially failed, ie I can keep it from going over 3 bar by limiting the temp to 75C and keeping min pressure at about 0.4 bar.

I presume that the air will have leaked and needs pumping rather than the diaphram holed - or am I just being hopeful!!

John

[Andy Hall]

Try turning off the heating and remove the dust cap from the Schrader valve on the expansion vessel. Release the pressure carefully as you would to let a car tyre down.

If water comes out then you know the answer to your question and a new vessel is needed. Otherwise, release the water pressure on the heating circuit completely and then precharge the expansion vessel with a suitable supply of compressed air or a tyre inflator. Finally pressurise the water side again.

If you do have to replace the vessel, they come precharged with nitrogen

.andy

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[JohnB]

Thanks.

This is going to be interesting! Hopefully that will save me the cost of a

13 litre expansion tank. Costly no doubt.

John

[Ed Sirett]

... to around 6 bar so you'll have to let some out.

A work around would be to drain a radiator in a spare room (if you have one), but don't bleed the radiator, the air in the radiator will act as a good expansion vessel until you can replace/add the real one.

[Andy Hall]

Is it integral in the boiler, or separate?

You can get separate ones of that size for about £15 so it's not too horrendous.

.andy

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[JohnB]

That is a brilliant idea!!

I may well make use of that as I am due to donate my prostate to the local hospital in a weeks time & may not have time to replace it if necc.

John

[JohnB]

You amaze me. I am getting used to my boiler costing a fortune.

A dreaded Potterton Flowshure+ hence integral but (for once) easily removable tank. Being Potterton it may be much more expensive than normal to get the shape that fits. If so could be a good idea to fit an external one for that price.

John

[Ed Sirett]

[Please don't reply at the top. ] If the one in the boiler is easily exchanged (they usually are very inaccessible) then the manufacturers replacement is worth paying the extra (probably double) over a generaic component that would have to be fitted elsewhere.

[IMM]

If you do replace it with a generic vessel, fit it on the return pipe.

[john.bunting]

I have just checked HRPC online (thanks for you commenting elsewhere that they had an online site). £197 for the correct potterton retail 13.5L expansion tank .....gasp ...... Even trade will be pricey. I see they have Altecnic 18L at £39. The max working bar allowed is 4 so still should be OK.

Looks as if they have to be fitted the correct way round. Would not have thought of that.

Perhaps it would be cheaper in the long run to put a well lagged radiator in the loft and keep it filled with air!!!

JohnB

[IMM]

Using a rad is temp solution. Use a proper pressure vessel.

[Ed Sirett]

Agreed, there are issues withthe air disolving into the water and coming out elsewhere, if nothing else.

[Ed Sirett]

What's the reason for that?

[IMM]

Cooler, and you will find that most system/combi boilers have them there anyhow.

[john.bunting]

Thanks for all the info folks.

A generic tank on the return it will be.

JohnB

[Shabs]

Any idea as to where i might find this car-type valve as i removed the cover but could not see anything... saw a silver covered rectangle (where the gas lights up) and below that some pipes, wires, and pump.

So back to the original question would i find the car-type valve if i removed the cover from the silver rectangular gas chamber?