Newbie - Hot Water & Radiator loss after drain-down

[ucsman]

Firstly, great forum guys - just been a voyeur and enthusiastic DIY'er, though never thought I would be posting for help.

Just had to drain down my CH to fix radiator pipe dislocation by my 2-year old. Now I have repaired, I have switched the central heating back on, I have no heat to radiators or hot water.

After the refill, all radiators bled, pump bled,

Combi boiler is @ 7 years old in house from new, Potterton Prima 60 B in garage - whilst the boiler lights from pilot to main burn, this only seems to occur for a couple of minutes

Header looks OK - water present and level.

Motorised valve sounds as though it is working,

Pump sounds as though working - getting hot along with pipework

CH has been down for a couple of days in total during part-time repair process. Not an expert on CH as you can see, but would appreciate any advice - out of ideas

Any advice welcome please (without liability of course) - if not or me, for the wife and 2 year old shivering cold at home.

 

[kevplumb]

I could be wrong (it's not unknown) but a potty prima aint a combi

i would start looking for vent point's

one assumes you locked the three port valve mid pos when filling

 

[croydoncorgi]

You're right Kev - it ain't! Combis don't have F&E tanks - full or empty.

Still - 95% certain system is airlocked somewhere. If the boiler fires and heats up to its thermostat setting in seconds, then there's no flow in the primary pipes to the motorised valves, etc. Let me guess - the boiler's in the garage and the valves, cylinder, etc. are under the stairs or in a first floor cupboard at the end of a long, flat pipe run from the boiler. Classic airlock territory!

Assuming you did not actually do a complete drain-down and then filled up with the motorised valve(s) closed, the first thing to try is to get circulation through the HW cylinder coil. Have you found and bled the airvent on the top of the cylinder coil? If not, do it, then try to get the system going on hot water only, with the CH turned off on the programmer. If the pump is noisy, put something under it to catch drips and loosen the big screw in the centre of the body. Does air come out or just water? Leave it loose for a while to see if the air will vent out that way.

 

[ucsman]

Thanks for the tips guys - now I really know how much I dont know. I did not have the 3-port valve in mid position (3 port is a Danfoss HSA3 - 2 outward labels manual and auto) when filling.

Croydoncorgi - have you been in my house? - fairly accurate explanation of the floorplan. I had thought about a bleed on the cylinder, but could not see anything apparent (apart from an approx 7cm cap with hex-head - is this the bleed?)

Would it be easier to drain/refill the system again - if so what would basically be the process. Last time, it is safe to say that I just ran the radiators and header out, replaced the pipework and turned back on the header to fill system.

Again - many thanks for the help guys - very much appreciated

 

[kevplumb]

the bleed points will be on the pipework
if you undo the one you describe you WILL get wet sounds like the immersion blank LEAVE IT ALONE

 

[ucsman]

Thanks for the warning kevplumb - most definitely will leave alone.
Will check for the bleedpoints on the pipework and loosen pump screw in morning to check for air.

 

[ucsman]

Croydoncorgi/kevplumb - just want to say thanks for the advice given.
Bled the pump and cylinder vent and hot water/radiators piping hot.

Sadly, the radiator I had to remove seems a bit cool so may be sludged - do you know of any fluid I can use. Seem to recall that there was a product that you can inject through a bleed valve. Whilst I could drain down again and remove the radiator, ideally would like to avoid this given my previous escapade

Many thanks again guys.

 

[croydoncorgi]

If the rad is cool all over, it's not likely to be sludged. Sludge normally collects at the bottom centre of the rad, so the top still gets nice and hot once the air has been bled out. I guess you didn't take it outside and flush it manually while it was off the wall. Unfortunately, there's no Magic Bullet (liquid form or otherwise) for desludging rads.

The reason the rad is cool MAY be some air still partly blocking a pipe or the system may be unbalanced. If you've not changed any lockshield valve settings, leave it for a while - any air should move into the top of a rad quite quickly. Then try turning DOWN the lockshield valves a bit on some of the other rads that ARE getting hot. The idea is to redistribute the flow in the system so that the 'bad' rad gets a fair share.

 

[ucsman]

Tried this and all is well now - many thanks for the top advice croydoncorgi over the last couple of days. You learn something new every day.

 

[COG]

Crydoncorgi, what do uou meen "combis dont have f+e tanks" ?

 

[croydoncorgi]

Theoretically, you COULD build a combi which would work on an open-top system, with an F&E tank. In reality, I don't think there ever were many such things actually sold and none still in existence. All now have a 'sealed system', with an expansion vessel built into the boiler. One of the key selling points of combis has always been that you get rid of the tanks in the loft. If you got rid of the cold water tank but were still left with the F&E, that would look silly!

 

[kevplumb]

worscter rings a bell (yeah i know i cant spell)

 

[COG]

As said Worcester have been doing open vented combis for years ,still do, BG used to fit them all the time before they discoverd the power flush.

 

[croydoncorgi]

Do WB still produce combis able to use open vent systems? Which models? I never came across one.

 

[kevplumb]

last one i did was a highflow a few years back
sure pedantic posted that they do a kit to open vent them