by The Heating Doctor »
Fri Oct 12, 2007 12:46 am
Sounds like what both of you need is a automatic by-pass valve this is a valve that fits between the flow & return pipework close to the boiler ie it makes a bridge between the flow & return. The idea of this (which is now mandatory under Part L of the building regulations since April 2006) is to perevent water hammer and excessive pump wear in the event of the TRV's in the heating system closing down. How it works is that your pump runs at a constant speed, when all the TRV's are calling for heat i.e. open you need all of the pumps speed to get the water around all the radiators, however as the TRV's start to close the pump is still pumping full speed until it is pumping against a closed circuit, the boiler shuts down and the pump goes through it's overrun again against a closed circuit, the pressure increases as will the noise and in a open vent system the water goes over the open vent, in a sealed system the pump goes through a real tough time and will reduce the pump life. When a automatic by-pass valve is fitted this senses the increase in pressure and opens up, thus providing an escape route for the pump. The water leaves the boiler through the pump, travels through the by-pass in to the return back to the boiler in a loop. As the pressure decreases because TRV's start to open again the by-pass valve closes and the water goes back along the flow to the radiators missing the by-pass. You will need a 22mm automatic by-pass valve costing no more than £30 + vat.