F&E tank/Pegler differential pressure bypass/thermostat

[pipedream]

I am a bit bitter and twisted, 'cause I have just spent 5K on plumber - looks fab, but we now have an external shower from the dripping flow and expansion tank (great for ducks, annoying to humans). The water is backing up the feed and the plumber has hot-footed it out of town (typical!). System spec is: HRM wallstar 15-20 oil-fired boiler with Centrecal 120 high performace indirect cylinder with de-aerator and bypass valve fitted. Sentinel X100 inhibitor was added. Central heating flow temp is 84 deg C, return temp is 78 deg C.

Correct me if I am wrong, but I think I may have eliminated the usual suspects: when the ballcock in the cold water storage tank is tied up and then drained, there is no changing level in the feed and expansion tank, which suggests that there is no problem with the coil in the cylinder (?) There is no change in the level of the F&E tank on heating/cooling and no airlocks in rads, both of which suggest lack of expansion (?). I have twisted the Pegler diff bypass valve in the hope that is cures the problem, but confess that I did not understand what the hell I was doing, and all it seem to do is relieve the pressure of my frustration for half an hour . Diff. pressure valve is the same model as screwfix sell (one with blue valve top)

Strange things happen: today when the Central heating and HW have been off for 5 hours, there was a sudden rush of water out of the F&E tank and then it stopped....eh? Does this suggest that there is an airlock and I have not found it, or sudden change in water pressure? And why is the dripping most prevalent 5 mins into the CH being turned on, lasting 40mins and then dripping is noticeably slower?

Can the diff pressure bypass doing anything to help (what should be the correct setting anyway??) and, would turning thermostat up/down on boiler help?

 

[kevplumb]

try lowering the water level in the f&e tank sounds like it's set to high

 

[wilhelm]

jeez kev, you aint cut and pasted that reply too often.

 

[pipedream]

try lowering the water level in the f&e tank sounds like it's set to high

thanks for that kevplumb, but that was the first thing I did sometime ago: bailed it out to pre-existing levels and bend the stopcock just to be sure, but two days later, drip, drip, drip.

What about diff valve

 

[ChrisR]

It doesn't make sense to me. I just thought I'd share that with you.

 

[kevplumb]

whats that chris ??

There is no change in the level of the F&E tank on heating/cooling and no airlocks in rads, both of which suggest lack of expansion (

now that bit dosen't make sense

 

[Slugbabydotcom]

For the sake of spending a fiver try fitting a new balltap as I suspect the one you have is passing water when the system is cold and as the water expands again it is overflowing as there isnt enough room for expansion with the extra water in the tank.

There is no change in the level of the F&E tank on heating/cooling and no airlocks in rads, both of which suggest lack of expansion (?).

Doesnt make sense to me either must be a red herring

there was a sudden rush of water out of the F&E tank and then it stopped

Here's my thoughts on this :-
Suggests pumping over! I cant tell you which way to turn it but I suggest you turn the diff by pass so that it opens more easily under pump pressure. It could also be blocked / siezed. There may be a vernier guage on the side to give you a clue although I am not au fait with this particular valve.
Would I be right in saying that this happens when all the TRV's have closed off because they have reached the desired temperature A solar heat gain or similar during the day could mean that all the rooms are at or above set temperature when the system comes on and if the by pass is closed the only way for the water to go is up the vent or feed depending on system layout resulting in water overflowing