hot water prob

[sammy128]

Hi all
I have a prob with central heating/hot water any help appreciated

First off a week or so ago I turned central heating off and set controller to hot water only. Hot water ok but a few rads got hot too.
So, I was told probably gate valve, anyhow I replaced it. Now I can get ch but no hot water at all. If I select hot water only, the boiler shuts down after a minute or 2.
The system is old but has always functioned ok, tho probably not ecconomically.
It is a potterton back boiler, gravity hot water.

I'm fairly sure I fitted the gate valve the right way round....help please.

I can leave ch and dhw on for an hour, rads get red hot, but feed to cylinder stone cold

 

[bellairaphon]

have you checked your motorised valve?

 

[maddog1964]

you cannot fit a gate valve the wrong way
the flow and return pipes for hot water on gravity should have no gate valve on it
sounds like an air lock check the tank in the loft for water if you drained some out its not filled up and the coil in the cylinder is often the highest point so the first to fail .

 

[maddog1964]

have you checked your motorised valve?

gravity so no mv

 

[sammy128]

No mv fitted. Just been searching the internet, someone with a similar problem has been informed, most likely air lock in cylinder coil. How can I vent this, no bleed nipple or anything...could I just loosen the nut, if so i'm not sure which one to loosen either. Could I just loosen both (one at a time) to see if air escapes?

 

[Agile]

In the normal and correct situation the flow pipe continues up past the top coil connection and thus any air is expelled that way.

If its not properly fitted then you could see if loosening the nut allows any air to come out.

Far better to correct the pipework though!

Tony

 

[sammy128]

Thanks maddog1964, maybe I used the wrong term gate valve. The valve looks just like a thru compression fitting 22mm except with spring loaded plunger enclosed, like a one-way valve. The valve has a direction arrow which I have fitted facing upwards from the boiler (the valve is fitted on pipe adjacent the boiler)
When I took the old one off it seemed ok, a bit gungy but the mechanism still worked, anyhow I thought I'd replace it cos I didn't want to drain the system down again if it was faulty. No difference, still no hot water

 

[sammy128]

Thank Agile, not sure what you mean regards routing of pipe work, I havn't altered any, the system has been in about 15 years, no problems till now

 

[Agile]

Its normal for the vent pipe to extent from the top cylinder coil connection up to the F&E tank. Air is thus expelled that way.

It sounds as if you have a non return valve.

They are not usually fitted and in most cases the gravity circulation would be too small to open against the spring pressure.

I suggest you remove the sealing disc inside and see what happens.

You still need a means of expelling air!

Tony

 

[sammy128]

I have removed the disc, stiil the same. No hot water just ch.
The top inlet cylinder coil gets hot, the bottom one stone cold. I loosened the top nut, no air in, just water.
Immersion heater works fine...good pressure at all hot taps.
Could I try back filling the vent pipe at the ch header tank, with mains pressure water, would that have a chance of clearing / blockage/ air. ?

 

[Agile]

Have you yet drained a bit and removed the two cylinder coil connections and looked into the coild and back into the pipes?

Its a favourite position for a blockage!

Tony

 

[sammy128]

the connections are real stubborn, I think the cylinder will crack if i go any harder...so nope.

I was thinking of cutting pipe and then removing cylinder and flushing with hose. Would that be a worthwhile thing to do?

(the top one was ok, comp. gland next to inlet, so loosened ok)

 

[sammy128]

Semi-solved !
Now I have hot water, but I have selected hot water only (on controller)
But the upstairs rads get hot as well, don't know how because the pump does not run when hot water only is selected. I suspect the one-way valve that I removed is the reason, but I aint going to replace now cos I'm sick of draining the system, its a pain...but I will replace tomorrow and see what happens.

I got thus far (to get hot water, the rads have always worked)

1)Disable boiler firing
2)Turn on drain valve slightly, not full flow
3)Leave water supply on, let it flush for a few minutes
4)Stop and start the pump several times for a few seconds each time

Imediately big gurgle noises, cylinder bottom coil hot (the system was hot previous because of rads working ok.)

Turn off drain valve

The bottom connection was always cold, the top connection warm...I knew straight away it was fixed...Err I thought!

20 mins later mad hot rads and hot water, in fact hottest ever been in 20 years, to hot to touch bottom coil in fact. (the boiler was set on highest setting)

But, like I say, now select hot water only, upstairs rads get hot as well. It must be the valve?? I hope...to be continued

 

[sammy128]

The water in my ch must be clean enough to make tea, its been drained and flushed so much these past few days. I know it may cause probs later...but what to do? I could do with changing rads anyhow. I'm delaying adding the inhibitor cos at 15 quid a chuck I don't want to have to drain again and lose it. I've used fernox cleaner, would you reccomend giving another dose before adding inhibitor

The exp tank is ancient, either zinc or galv, its flaking to bits, the ball-cock looks like an onion bargi. There must be some real gunge in the system, I ought to change the tank as well