10 year old machine always worked flawlessly. Now will fill normally at start of cycle, start agitating, then at a random time while still agitating (varies each time) will start filling again. Sometimes it stops filling and continues only to start filling again 30 seconds later. Others it just keeps filling. Result is always overflowing machine. Does not fill when switched off (so can\\\'t be mixer valve). Could a blocked pressure tube cause these random fillings during the cycle?