rising water in F & E tank, rising blood pressure too

21 Mar 2006
Reaction score
United Kingdom
HELP...... Totally stumped. Water was dripping from F & E tank overflow . F & E tank is below the level of the cw tank in the loft. Took all rads off walls & flushed them through with a power washer in the garden. Refitted rads and put Fernox SD40 into the F & E tank and ran the system for a few days before draining and putting the neutraliser in the F & E tank. Ran the system for a few hours and then drained / refilled system 4 or 5 times to flush out all sludge / sediment. Pipework now clear ( magnet not sticking to any of them ) Water level in the F & E tank still rose & overflow was still dripping so replaced the HW tank yesterday as all symptoms suggested that the coil may have been burst. Got up this morning to the sound of dripping water from the F & E overflow ... Turned the heating & hw off & drained down the water in the F & E tank and noted the level in tank. Just been up in the loft for a nosey and the water level in the F & E tank has risen 1.5" over the last 3 hours with the inlet valve closed and the ballcock tied up. Water is definitely coming back up the heating supply pipe into the F & E tank. Any idea on where this water is coming from ? What should I do next ?
Sponsored Links
Unfortunately it sounds like your heating coil is holed - probably due to the flushing.

Your only course of action is to replace the hot water cylinder.

This happens to me occasionally when power flushing a system prior to installing a new boiler - it's really a latent fault that would have happened sooner or later.
Eliteheat...... I replaced the HW cylinder after flushing the system ( checked the coil wasn't holed before fitting the new hw cylinder ) and the problem with the water flow still exists. RGBD
is you system gravity hot water and pumped heating or is it fully pumped?

just saying that if you popped a HE cylinder on a gravity hot water it can pump over

am probably wrong but the fault you describe us a right pickle of a one quite flummoxed by it
Sponsored Links
Corgiman......Hot water gravity ?? don't know what that means as I'm a newbie to this heating/ plumbing thing. I can describe the system though.

CW tank and F & E tank both in the loft. Both tanks sitting at the same level but F & E tank is below water level of CW tank. HW cylinder in airing cupboard below these two tanks. Boiler downstairs in kitchen, Pump in airing cupboard beside HW cylinder. Water flows from the boiler up into the loft and through an Aerjec II ( thingy that has the cold feed pipe from the F & E tank and also a vent pipe coming out of it.) It then goes down to the pump then through a Honeywell valve (that has a lever that you can select manual or automatic) through the coil in the HW cylinder ( or through the bypass into the rads ) and on to the rads. Hot water has to be on before you can turn the heating on. Would you like me to post some photos ( if that would help ) ?? Cheers Rgbd ....
Bugger its a fully pumped system

well I am plum out of ideas

maybe lor is right and I am rubbish!!!

sorry mate :oops:
Cheers Corgiman ...... But don't give up , I'm sure you or someone will come up with a cunning plan eventually :D
am sure one of the regs will have a brainstorm about it

i am still thinking :p
Perhaps coil in new cylinder is also suspect. Was the previous new one not faulty and had to be replaced? You say in previous post that you tested coil by plugging one end and blowing into other. What pressure were you able to generate? Perhaps not enough to cause coil to fail but when installed it failed under pump pressure. In previous post the water seemed to be flowing in opposite direction with pump on and overflowing cold storage tank. Suggests pump is delivering sufficient pressure to overcome difference in water level between CHT and F&E tank.
just a thought

the overflow from the main cold water storage cistern doesnt terminate in the feed and expansion tank does it??

(runs around grabbing at straws :LOL: )
Just a wild idea, if you set the zone valve to manual does it still do it?

When original HW Cyl was insitu the water was flowing into the F&E tank when the CH & HW were switched off. :(

When the replacement HW Cyl was insitu the water was flowing into the CW tank and the F&E tank had water continually running from the filling valve and continually disappearing into the CH system. :(

Now the 2nd replacement HW Cyl is insitu the water is flowing into the the F&E tank when the CH & HW are switched off at a rate of approx 0.5" per hour :(
I turned the CH & HW on approx 3 hours ago and just been in the loft again to look and the water level in now approx 3" higher than it was after I emptied the tank this morning.

Don't know what pressure was put into the coil when testing , but the max working pressure of it is 3.5 bar.

Not sure what you mean by " Suggests pump is delivering sufficient pressure to overcome difference in water level between CHT and F&E tank " :?: CHT ? :oops:
Corgiman... The overflow from the CW tank runs straight through the loft and through the wall under the eaves. Keep thinking though !!

Expertboy...... I did put the zone valve to manual when I was filling the system but I put it back onto Auto. Haven't tried monitoring the water level with it switched to manual. Would that make any difference cos the CH & HW were switched off anyway ?

Can I run my heating with the zone alarm on manual all the time ? What does it do anyway ? does it tell the CH boiler when to fire up ??

Wil monitor the water level with the zone alarm at manual tomorrow out of curiosity ( too cold to switch the heating of now , it's freezing outside )

Cheers Gents..RGBD
My reading was that the water level in the CWT is above water level in the F&E tank before the problem arose.

With a faulty coil and CH pump off the water levels will try to equalise and flow from the CHT into the cylinder into the coil and raise the F&E to ovweflowing.

If you switch the pump on this will increase the pressure in the coil particularly if you have a restriction on the return to the boiler. The additional pressure in the coil due to the pump MAY overcome the difference in the water levels and reverse the flow causing the F&E to draw down and the HWT to fill up and perhaps overflow if taps/flush is not being used. However pump will not run continuously as the controls will switch it off when the stats are satisfied.

I was suggesting that your new tank was faulty, perhaps a faulty batch as the previous one was faulty.

You could try draining down your CH and disconnect the pipework from either end of the coil to see if any water continues to run out. If it does then another faulty coil (seek compensation from manufacturer for effort wasted), if not at least you have ruled out one possibility.
Joebloggs.... Sorry , I forgot to say that when I drained the HW Cyl I noticed that the valve on the feed pipe from the CW tank to the HW Cyl was passing so I turned the CW mains coming into the house off and drained both the HW & CW tanks. The water level in the CW tank is normally above the level of the F&E tank. Can't remember if the CW tank was full or not when I turned the heating on when the first replacement HW Cyl was in place. :oops:

Another observation... when the hot water and/or the heating is switched on the pump runs all the time , only the boiler switches on & off when required by stats.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links