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water coming from rad.cap

we are de-winterising our narrowboat. We have filled up the water tank and every time we turn on the water pump, the radiator cap on a tank in the engine well leaks waater. We have replaced the cap, what else can we do please?

Asked by: peter  | 8.29pm, Friday 11 March

WW says:

I am a little confused as to which tank is leaking. The radiator cap on a tank in the engine room- not quite sure how that is connected to the (presumably domestic) water tank and pressure pump.
If it is the engine (or central heating) expansion tank- then it could be due to trapped air, which needs to circulate out, or, if filled to the brim, as it heats up, it will leak, as the water expands, if there is no rooms for it to expand to!
If the calorifier is leaking into the engine bay, it may mean air has not been purged from the system, the PRV (pressure release valve) is in the drain position, or is faulty.
I am sorry- I cannot be more specific. If you can email pictures of the tank, etc. to mark.langley@waterwaysworld.com then I might be able to help solve the mystery

Mark Langley  | 11.42PM, Friday 11 March

As part of the winterisation process did you check the concentration of the antifreeze in the engine cooling circuit?
It sounds to me as with the extremely cold winter we have just had, that coolant has frozen and split the coil within the calorifier, due to worn out or insufficient antifreeze.
When the water pump runs it pressurises the water within the calorifier which is leaking into the engine cooling circuit.
I would advise not drinking or cooking with the domestic water until the fault has been remedied since there is a risk of contamination with antifreeze from the engine.

Rupert Smedley  | 9.50AM, Wednesday 23 March

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