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No Hot Water Or Heating Following A System Drain Down


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Hello,

 

I wonder if you could help me. (sorry if this is in the wrong place, i'm new to the forum)

 

I've got some issues where i'm not getting hot water or central heating.

 

This has come ever since I drained the heating system (open vented with 2 tanks in the loft) down to fix a leaking rad.

 

I beleive i might have an airlock in the system ( when refilling i made the mistake of bleeding the upstairs rads first).

 

I've tried draining the system again and refilling (this time bleeding from the bottom) but still no joy.

 

The boiler (Glowworm Micron 50ff) is firing for about 5 mintues then cuts out, at this point i get large amount of banging noise from the airing cupboard.

 

Looking inthe airing cupbaord it looks as though i'm not getitng hotwater to the cylinder. The pipes going into the pump are very hot but the other side are warm (ish).

 

I've bleed the pump, i think (i've released a lot of air out of it), but this doesn't seem to have resolved any thing.

 

It looks like it could be a new pump needed but it was working fine prior to draining so i'm hoping it's not now needed. 

 

If it's an air lock how can i clear it? drain it again? Backblast the system from mains cold?

 

I've done a fair amount of reading online and have familiarised myself with things (still only a DIYer) but i'm really getting stuck now and the wife will go mad if the weather turns and the kids haven't got heating.

 

 

Many thanks Richard

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Rob_the_rich

Welcome to the forum Richard

You could try back flushing with mains, but it is risky if you are not absolutely sure what you are doing.

Make sure the little tank in loft has water in it, ball valve might be stuck

Make sure the pump isolating valves are open, fully anti-clockwise then clockwise 1/8th of a turn (so doesn't get stuck, same with most taps/valves left open).

Manually open the levers on the motorised valves while system is running

Bleed all radiators

Look for any manual (thumbwheel) air vents, also check the plastic caps of automatic air vents are not fully closed

You could try isolating the pump and putting it upside down for a burst, but check the little tank in the loft is not pumping over too much and splashing water everywhere

Bleed the pump when running, loosen the big screw and catch any water

 

if it all works, don't forget to add inhibitor

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Hi Rob,

 

Thanks for the response,

 

The ball valve is ok and the tank is full.

 

I've not checked the isolating valves or the air vents but these were changed from when it was working but, i'll check them all the same (I've not seen an air vent yet). Can i ask where would i most likely find any air vents (ie. in loft, by cylinder or boiler etc).

 

Would i need to bleed the pump mulitple times because i've done it before an a lot of air came out? is it best to do this when the pump is hot or cold.

 

Thanks again for your response

RIchard

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ProDave

It could of course be a poorly designed system that lacks enough bleed points. e.g in my previous house there was no bleed point on the flow and return to the cylinder, so the only way to bleed it was crack open one of the compression joints.

 

Look for any loops of pipe that go up then back down without a bleed point at the top.

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Doc Hudson

When was the system last previously flushed or drained. If it has been a long time it may be sludge in the pipes or radiators that has been disturbed and is now causing a blockage else where in the system. Are all of the manual radiator valves and thermostatic valves fully open to maximise the flow while refilling. Have you had regular doses of inhibitor fluid or sludge remover added to the system to help dissolve contaminate building up. Have you manually opened all motorised valves on the system whilst it is refilling to ensure flow down all pipe branches.

 

Doc H.

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Had this problem twice on the same system after drain down.

 

There was a loop in the paperwork from header tank to cistern.

 

First time I loosened the return input connector at the cistern and this cleared the air lock.

 

Second time I did the same but installed a tap at that point so any further air locks were easily fixed.

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Thanks for the responses to this, it's great to know theres a community willing to help.
 
Just an update on this.
 
Today isolated the pump and turned the heating and boiler back on. then after about 2 minutes it sounded like a surge of water clunking through the pipes (i was listening in the airing cupboard. i had my finger on the pipe when the water went through it was so hot it burnt my finger but the heat was gone quicker than it came. after that the boiler stopped and now hot water.
 
@dave2 - sorry to be dumb but i'm not overly sure which pipe is which when it comes to flow and return, and when you say the cistern do you mean the cylinder in the airing cupboard?
 
@Prodave - How would I identify a loop?
 
@do hudson - I had previous drained it about a month before,  had a cracked radiator due to sludge so i drained the system down, took all rads off flushed them with a hose and refilled the system, this didnt cause any issues, i only had to drain the system again due to some leaky joints on the rads which needed some more ptfe tape and tightening.
 
I've got some images of my airing cupboard but i cant find how to attach them
 
from what i can see i've got no vents on any pipes.

 

 

 

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NozSpark

It might be worth shutting all the rads off (but leaving one open) and running the system for a few minutes... Try each radiator in turn starting with the upstairs ones.

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ProDave

A Loop I was referring to was any bit of pipework that goes up, along a bit then down, with no means to bleed air out that collects at the top.

 

sounds like your air lock has cleared now so you will probably be all right now.

 

Just for future reference, you shouldn't need to completely drain the system to remove a radiator. Shut off both valves both ends of the rad and you can drain and remove the rad while leaving the rest of the system full.

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Rob_the_rich

Today isolated the pump and turned the heating and boiler back on.

why?

the pump needs to be running (with open isolation valves) to transfer the hot water around the system. With the pump isolated, the boiler becomes a kettle and literally boils the water.

My earlier suggestion was to re-fit the pump upside-down temporarily, the isolation was so that you could do the re-fitting without getting too wet. The reverse flow might cause any air block to clear.

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The cold water feeds the bottom of the hot water cylinder direct from the header tank.

My problem was on the domestic hot water and not the radiator part but was caused by a loop in the pipework.(as described by Prodave)

Thanks for the responses to this, it's great to know theres a community willing to help.
 
Just an update on this.
 
Today isolated the pump and turned the heating and boiler back on. then after about 2 minutes it sounded like a surge of water clunking through the pipes (i was listening in the airing cupboard. i had my finger on the pipe when the water went through it was so hot it burnt my finger but the heat was gone quicker than it came. after that the boiler stopped and now hot water.
 
@dave2 - sorry to be dumb but i'm not overly sure which pipe is which when it comes to flow and return, and when you say the cistern do you mean the cylinder in the airing cupboard?
 
@Prodave - How would I identify a loop?
 
@do hudson - I had previous drained it about a month before,  had a cracked radiator due to sludge so i drained the system down, took all rads off flushed them with a hose and refilled the system, this didnt cause any issues, i only had to drain the system again due to some leaky joints on the rads which needed some more ptfe tape and tightening.
 
I've got some images of my airing cupboard but i cant find how to attach them
 
from what i can see i've got no vents on any pipes.

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