Running water!

This picture marks a massive step towards completion of the kitchen rebuild and my return to more model making - unless Mrs. Woody has other plans!

However getting to that point took both Phil the builder and myself on a journey neither of us had been on before. Having installed the waste pipes - always best to get those in before the running water is connected - Phil connected up the water. Testing the connections, the cold ran and the hot ran, both without leaks. Great! Turn the two on together and all was well for two minutes before the overflow at the top of the house started gushing! Not great! Phil had never seen that before and neither had I. What was going on? We had running water in two places! Phil had a theory which was backed up by my perusal of the internet. 

The issue was that the cold water was being supplied straight from the mains at a high pressure. The hot on the other hand was supplied from the hot water tank upstairs using gravity and its pressure was low. Inside the mixer tap, when both the hot and the cold were turned on full, the outlet of the tap could only allow a certain amount of water out which was less than the water being supplied by the cold and hot inlets. Therefore the cold water, with its much higher pressure, was able to backfeed into the hot pipe and push the water back into the hot water tank. The hot water tank then needed to expel the excess water which it did through its feed from the cold water tank in the loft. The cold water tank then had to get rid of the excess water through its overflow pipe hence the gushing water we saw outside.

The answer was a one way valve on the hot supply which Phil had one of in his van - almost as good as WMD Stores! Once fitted, the problem was solved and we only had running water in the sink!