While my PRV gen­tly weeps...

Canal Boat - - Back Cabin: - TONY REPLIES… IANSUTTON, via CB’s

QThe pres­sure re­lief valve on my calori­fier seems to con­stantly weep when the wa­ter is be­ing heated via the im­mer­sion heater when I am con­nected to my shore­line power. Could the PRV be faulty?


When­ever cool wa­ter is heated it ex­pands. The ac­cu­mu­la­tor should take care of most of that by pro­vid­ing a space for the wa­ter to ex­pand into with­out rais­ing the pres­sure to a sig­nif­i­cant de­gree. If there is no air space (air is com­press­ible, wa­ter is all but not) in the sys­tem and you have closed taps, the pres­sure in the sys­tem will rise very quickly and cause the PRV to drib­ble, this is nor­mal for a boat with no ac­cu­mu­la­tor or ex­pan­sion tank.

You could try fit­ting an­other ac­cu­mu­la­tor on the hot side of the calori­fier pres­surised to 1.7 bar so it acts as an ex­pan­sion ves­sel. If you fit a PRV of a higher pres­sure than that rec­om­mended, you stand a fair chance of split­ting the calori­fier by pres­sure from the ex­pand­ing wa­ter.

Once you are sure the ac­cu­mu­la­tor is pres­surised as I in­di­cate, the next thing to do is to fit a new PRV set to what­ever pres­sure Sure­cal rec­om­mend. Some have a rub­ber washer like a tap washer and this can go hard.

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