Hot water being pumped out of overflow on indirect system

Simon Dyer · 4 Jan 2007

Hello wonderful helpful plumbers

. I have a indirect sysytem with 3 pipes from the boiler, 1 hot feed to radiators and tank and 2 returns, the pump is on the radiator return. During the summer it gradually stopped heating the hot water via gravity and water would only flow around if the heating was on (pump forcing it through the coil I quess) This was fine as I was lazy and just used the immersion heater and thought all would be ok as winter is approaching and heating will be on and water will get hot. Well this worked for a bit but now I get continous air locks in the heating causing hot water to be pumped out. The return to the pump from rads is the one that fills with air as the water trickles over like a waterfall, causing the bioler to whoosh as the water enters it. When I get the air out it will run for 2 hrs heating all rads then she just pumps out with a lot of whooshing etc.
(could be when the thermostat closes the 2 port valve closes when the hot water is to temp ?) Originally I believed I had a primatic system as could only find one tank utill I drained it today when I found a little one hidden by lagging

.
I think I may have a blockage somewhere as the I quess the gravity hot water problem is maybe related to the pumping out.
Any suggestions of a fault finding process or where to look first ?
Thanks in advance

Simon Dyer · 4 Jan 2007

shameless bump as I need to work on it in the morning

Slugbabydotcom · 5 Jan 2007

I found that very hard reading which is probably why no one else answered.

I get continous air locks in the heating causing hot water to be pumped out.

you just dont seem to be specific enough about anything.

Well I got the jist of it so heres a few ideas of things to check and places to look.

Is there any water in your F&E tank?
Is the vent pipe over this tank where the water is 'pumping out' ?
Try turning your pump speed down a notch or two .... See what happens
Your system could be sludged up.
Your zone valve might not be working right.
Fitting a de-aerator where the feed and vent pipe are connected to it eliminates most air problems.
Old pumps especially grundfos ones have been known to leak air into a system. Doesn't happen often but it does happen

Simon Dyer · 7 Jan 2007

Thankyou for the reply. I think the problem is with the hot water side of things which I will try to describe ....wait for it

The hot water stopped working by gravity in the summer as I described earlier. What I have noticed is that the return from the cylinder gets hotter than the supply starting from the boiler and going up the return ( it is working the wrong way round!). The pump is on the CH return which in theory should cause supply to the HW to be pumped as well when the valve is open.
The feed is on the HW return and expansion on the CH/HW supply.
I have had the tank out and it doesnt seem to be blocked and I have checked for blockages near the boiler and the 2 port valve opens.
I had it running for 4 hrs then it pumped a lot of air in, as soon as i switched the pump off the cold water from feed tank filled down through the hw return pipe as it should.
I know i am awful at describing my problem but I am cold and need a little help .thanks

fitz1 · 7 Jan 2007

can you show pictures.sounds like a mixed bundle of fun. probable piping prob.where are your zone valves, and what type ,2ports ?

Duzzer · 7 Jan 2007

It's a problem caused by the pipework blocking over the years and you have got to a point where the system cannot function it's having a heart attack.
You say it's gravity hot water so your system is going to be over 20 years old so it would be better to rip out and start again because you'll be throwing good money away trying to get a quick fix. If you wanted to have a go of getting it working i'd say it sounds like a blockage on the return somewhere that's why your gravity is not circulating and also pumping over. It will be where the cold feed enters the system also you'll prob have a slow filling system that's why your having problems with air all the eventually your cold feed pipe will block totally and it will need cutting out and blockages removed. That's why i'm sayng cut your losses and start from scratch

Simon Dyer · 8 Jan 2007

Ill get some pictures later when I get home from work, replacing pipework is no problem for me to do myself, just needed an idea where to look.
I will chop T jiont where the cold feed enters the system on the hw return.
Yes its aged and on its last legs and will be replaced in the summer
thanks for the replys

Duzzer · 8 Jan 2007

I have quite a powerful magnet i run along copper pipework if you feel the magnet trying to stick to pipe that's where the blockage will be because copper isn't magnetic but the blockage will be steel of the rads which is

corgiman · 8 Jan 2007

Duzzer said:
I have quite a powerful magnet i run along copper pipework if you feel the magnet trying to stick to pipe that's where the blockage will be because copper isn't magnetic but the blockage will be steel of the rads which is

well not the steel but the magnetite, but you are on the right lines

Simon Dyer · 8 Jan 2007

A quick update,
As soon as the 2 port valve closes to HW cylinder she gurgles and pumps out like mad so there must be a block in the single CH/HW supply from the boiler or is there a greater chance that its the HW return as suggested ?
Thanks

Duzzer · 8 Jan 2007

Magnetite is the name for the sludge which is very fine iron filings that is the steel from the radiator if you leave it in a clear bottle it will fall to the bottom and water will be clear run a magnet up the outside of bottle and the filings will attach to it.
The blockage will still be on the return when the zone valve turns off there's no path back to boiler so it'll go up open vent pipe. It will be partially blocked not fully blocked.

Simon Dyer · 8 Jan 2007

Thanks, I will slice her out in the morning and report back.

Simon Dyer · 9 Jan 2007

Success

Blockage was where you said it would be + a lot of sludge at the bottom of both returns, but I think the main problem was the completly blocked HW/CH feed pipe

No wonder things went a little strange when the 2 port valve shut, it was pumping back to front and through the cylinder.
Thanks for your help and patience Simon

Duzzer · 9 Jan 2007

Glad to see I havn't lost it. It will build up again you need to get to the root cause,ideally rip out and start again when you have the time and money,then clean out new system to pevent future blockages.

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Hot water being pumped out of overflow on indirect system

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