under sink water heater!

[shead]

I have an under sink water heater.....problem is its cosntanly blowing off water out the blow off valve. its an "Atlantic " water heater. i turned the heater off for 2 days and its still letting water out every 5 minutes or so. very strange as i know the blow off is used to allow for expansion. looks to be piped perfectly. Any ideas???? Im thinking it maby just to much water preasure from the mains...does it just need reduced???

 

[Biggles..]

What size in litres is it,does it have it's own little expansion vessel,the blow off is sometimes temp and pressure but if it's off it has to be pressure causing it.

Normal cause is not enough room for expansion,or flat vessel.

Under 15litres won't need a vessel but normally need at
least 2metres of pipe between heater and nearest cold water draw
off.

 

[JPC]

had this once..it turned out the Street Pressure reducing valve (severn trent property and very big, under the pavement and served the whole neighbourhood) had stopped working

i measured the pressure at 6 bar and hence it was blowing all the time

could it be that? or a knacked blow off ?

 

[shead]

yea its under 15 litres..no seperate vessle. sounds rite enough tho 'ICGS' yea.there is only bout half a meter between mains coming in and blow off. dont have much room to change that tho! would reducing the preasure cure it because there is an isolating valve on mains. No its not a faulty blow off 'JPC' cause ive just replaced it and same thing happening tho the mains is strong yea. Thanks for the replies so far lads.