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

 

[SimonG]

What pipe size you got going to the rads?

 

[wickers]

I unscrewed the drain cock a few turns. Water was spraying at pressure through the sides of the draincock that normally leaks when you drain the system. I believe that the mains water was getting into the system because I loosened one of the valves where it screws into the radiator (excuse the lack of proper plumbing terminology) and water sprayed out a quite a force.

If this method of refilling can be done it would seem to solve alot of problems of airlocks in open vented systems

 

[wickers]

The pipes are all standard 15mm to the radiators and 22mm between radiators.

 

[quality]

What you need to do is drain down completely (all air vent/beeds open on all rads) then re-fill slowly and I mean slowly Just a gentle trickle from the f&e tank (all air vent/bleeds still open until water expels) 3 port valve set to manual With the system not running.
It may take 2-3 hours but that's what it can take maybe even longer.
Ensure all rads are all bled as well as the cylinder before turning the system on

 

[wickers]

Thanks for the reply.

1. How do you bleed the cylinder?
2. Are all radiators bleeds left open when refilling (with cloths under to catch escaping water) ?
3. Is the system refilled slowly by controlling the flow of supply into the f&e tank?
4. I cannot find anything on the system that looks like an air vent (can these be added to make life easier in future)?

Ta

 

[dontknowitall]

1. The cylinder contains only the hot water for the taps. (Inside is a coil connected to the heating circuit which will drain and fill in the same process as the heating system).
2. No.
3. Yes. It might not be necessary though.
4. There might not be an air vent. Wouldn't necessarily make life easier.

You might not have an air lock as such, just air in the system which will be pushed out as you drain and re-fill.

 

[wickers]

PROBLEM SOLVED !!!!!

When the system was drained and refilled I did not open the radiator bleeds. This time a thorough job was done. All bleeds opened and the system allowed to drain (until no air could be heard being sucked into the downstairs radiator bleed valves) and no water emerged at the drain cock. The system was refilled and each radiator bled starting at the bottom radiator. The bleed was opened on the pump until water emerged.

Switched the power on and guess what? NO IMPROVEMENT !!!!!!

I decided to put the original pump back in as this was only changed as a process of elimination.

Switched the power on....PERFECT!!!! ALL RADIATORS HAVE BEEN HEATING UP TO THE POINT THAT YOU CAN'T HOLD YOUR HAND ON THEM. The boiler has stopped cycling as well.

The new pump was noisy from the start and I just put this down to being more sensitive to the air pockets. The "new" pump from Screwfix had some plumbers notes inside the box and so was obviously a return.

Thanks for all your help guys. I appreciate you taking the time to help us out. :winkiss:

Wickers

 

[GQuigley67]

glad you got it sorted

 

[dontknowitall]

Thanks for the feedback! Thought it was the pump!!

 

[Simon F]

another success story :hurray:

 

[quality]

older open vent system can be a real trouble to bleed / purge all the air. Its an experience thing and there is no hard and fast way of working on older systems as we all have our own methods. Whilst is don't agree with previous statements (dkia no 2) I am glad you are sorted out