Hot water in header tank??

While filling the loft in my new house with all the rubbish you never need but (she!) can't bear to throw away, I noticed that the Central Heating header tank contains steaming hot water (causing lots of condensation on the underside of the roofing felt)! It seems that when the pump is running, even if I run it at minimum speed and both hot water & radiator control valves open, the pump if forcing hot water up the Vent pipe in to the header tank??? The pump is mounted horizontally with the Vent & feed conneting to it via a horizintal feed from the boiler.
What are the recomendation for Vent/feed/pump postioning and head? As I don't know the history of the systen it's possible this is an installation fault? Advice greatly appreciated.
Bert
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the
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http://groups.google.com/groups?selm 0b11bb.0210270552.4f0023f5%40posting. google.com
-- John Stumbles -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -+ What's afoot? Twelve inches, as a rule.
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the
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The feed pipe from the header tank should be connected to the return on the system.
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Only on boilers pre-1980. Modern boilers (i.e. those without cast iron style water jackets) have a large pressure differential. If you connect feed to the return and vent to the flow, you will almost guarantee pumping over, as even a small pressure differential translates to a large head difference.
The more recent gravity system for modern boilers involves having the sequence like this:
1. Boiler flow. 2. Vent 3. Feed (no more than 15cm from vent). 4. Pump 5. Zone valves. 6. Boiler return
There must be an unzoned path from the feed to the boiler return. This allows feed water to find its way to the boiler to quench it when boiling (the section between the boiler and vent will contain steam, so can't be used for this purpose). This means either using diverter zone valves (which don't have an off position) or a permanent bypass (not an automatic bypass valve).
These rules don't apply if the boiler is suitable for sealed pressurised operation, as boiler safety devices provide equivalent safety by cutting the power if an overtemperature or water loss occurs.
If the feed and vent are not within 15cm of each other, then this is the likely cause of the pumping over. It may have the ancient system of feed on return, from when the system was installed, but not updated when a modern boiler was fitted.
Christian.
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Christian,
Christian McArdle wrote:

style
as
I can confirm it is a modern'ish wall mounted boiler - Ideal Classic

This seems exactly as it is and the Feed is about 10cm from the Vent.

(which
This does not appear to be present but I woud have thought it is not the cause of the over pumping?

on
Its does look like the boiler has been replaced at some point but all seems OK from the installation overview outliuned above. Any other clues much appreciated.
Bert
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This is quite unusual then. Possibly some sort of restriction in the feed pipe, or something. You might find it is just marginal and you can cure it by making the vent pipe curl around a bit higher than it does currently.
Quite frankly though, gravity fed primary systems are a PITA. If the boiler and other devices support it, I'd be tempted to rip out the tank and replace with a sealed pressurised system. You can get a kit for about 50 quid, with filling loop, expansion vessel, pressure relief valve and pressure gauge.
Christian.
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5a. Radiators!

As Christian says, something very strange going on then. I'd check very carefully that nothing else has been tapped into the vent pipe. Try temporarily lowering the level in the header tank, to see if its just marginally got enough head to be pumping over (boiler off so you've no risk of over-heating if you drain out too much water). If so a small extension to the height of the vent pipe might be an easy cure.
I'd also be very concerned about corrosion issues if you think the system has been pumping over for a while. I'd drop one of the rads off to see if there's a build up of sludge (i.e. the corroded away insides of your radiators!)
--
Steven Briggs



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wrote:

Are you sure it is pumping over via the vent pipe, i.e. have you actually seen the water exiting the vent? I ask because it is also possible for hot water to get into the header by reverse flow up the feed pipe. It happened to me, see http://groups.google.com/groups?selm4367b2f.22339974%40news.demon.co.uk
It's worth pointing out that "pumping over" has a seriously bad impact on your roof timbers if left uncorrected. Turning the pump speed down could be a short term palliative.
Other posts on "pumping over" here http://groups.google.com/groups?as_epq=pumping%20over&as_ugroup=uk.d-i-y
-- Phil Addison The uk.d-i-y FAQ is at http://www.diyfaq.org.uk / Remove NOSPAM from address to reply
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