Nearly no hot water and heating since refilling system

[wickers]

Helo to all (I'm new to this forum),

My system is basic gravity fed, hot water tank, 3-port valve etc,

About two years ago the system was cleaned (Sentinel X400), all radiators removed and flushed out and new Vailant bolier fitted.

System was working great. I drained the system to change a downstairs radiator valve and refilled.

Now, just about one upstairs radiator manages to get warm. All other radiators have hot inlets but return pipes out are stone cold. The boiler constantly fires up, reaches max temp in 10 seconds and cuts out. The hot water only just gets luke warm after being on for one hour. The main return pipe back to the boiler gets warm (but not hot).

I have tried draining (complete system and all radiators) and refilling. I have tried a new pump.

I have refilled the system by using mains pressure to force water up through the drain cock. WHEN I DO THIS NO WATER EMERGES INTO THE COLD WATER TANK IN THE LOFT ?????

The 3-port valve seems to switch between CH and DHW OK.

The cold water supply from the header tank is OK (because all radiators can be bled OK).

Any ideas to what's causing the problem would be most appreciated.

Thanks

Wickers

 

[GQuigley67]

sounds like an air lock my friend, quite common on open vented systems and can be a pain, try shutting all radiators apart from a few, see if the pump can force the air to they rads and then bleed them. Listen for the bubbles when your doing this you can usually hear them

 

[GQuigley67]

sorry didnt read your full post


is your system sealed or open vented ?? sounds like circulation problems anyway

 

[wickers]

Hi GQuigley67,

Thanks for the quick reply.

The system is open vented (my mistake - left that detail out).

Wickers

 

[dontknowitall]

Gravity and 3-port = open vented (I think!)

I'd go along with air in the system.

If you open the pump bleed valve (large chrome screw) and have a towel to hand, water should come out. A 3mm screwdriver will mean you can turn the motor (not when it's running!) and if it turns easily then you know it's not seized.

It sounds like a pump problem (heat can't get away from the boiler quickly enough so its thermostat kicks in) and bleeding the pump might well fix the problem. You'll also need to check pipework for other bleed points if they're fitted as air might be in these too.

If one side of radiator pipes are warming then it again points to a circulation issue.

 

[wickers]

I can get each radiator to heat up individually with all others turned off. Although, you can't get them too hot to touch. I thought that using mains pressure via the drain cock would move all air up into the header tank? When I use this method nothing (water or air) comes into the header tank. Does this mean a blockage some where? Strange that there is at least partial flow to all radiators????

Wickers

 

[wickers]

Water does dribble from the pump bleed valve when opened. I have also tried a new Wilo pump with no improvement.

 

[GQuigley67]

how big is your system? what size of pump did you fit ??

when you said that backfilling with the mains didnt work thats why i thought it was sealed system lol

when you do each individual rad seperately can you hear bubbles rushing through the pipes/rad ??? have you bled them ?

 

[wickers]

System size- 3 bed semi - 9 rads
Pump - Dab 5m head
Radiators - Each one was bled after refilling system. When the pump fired up you can here some gurgling and a few small 'wooshes'. When I try the bleed valve now each radiator has no air escape.

Backfilling with mains - I'm confused about this one. I thought that the mains pressure should push all the air out of the system and eventually push all the air bubbles and water into the header tank....but no air or water appears at the header tank ??? If it's open vented surely the mains water should come gushing out into the header tank (through the pipe that feeds into the pump)???

I have now managed to get one radiator (furthest from the pump and boiler) to get nice and warm. All other radiators are closed. Does this now prove that there are no blockages and the problem is an airlock somewhere?

 

[Simon F]

with the mains pressure was any water flowing?
the rubber washer is designed to close against flow, you might be pushing it shut with the mains pressure