valve stuck?

[breezer]

no, just if we try the c/h

posted at 16 05

its lovley amd warm in here, radiators on Marvelous!

turns out it was the pump, when the bg man took the motor from the body, the impellar was smashed in 3, that is the top had come off from the impelar, and what was left had a chunk missing (still in the housing but not where it should have been)

 

[masona]

Are all combi boilers works the same way regarding that hot water do not need pump to run which only need water pressure ?

So the pump is for heating only ?

 

[boilerbeasty]

It is on my combi. It also seems that the three way valve on mine is hydraulic (i.e. no motor) so as long as theres enough mains water pressure, it will switch the CH circuit to pump around the secondary heat exchanger instead, transfering heat to the cold water which then gets hot and comes out of the taps. Of course, you still need the pump to push water around the CH circuit so it goes through the secondary heat exchanger.

 

[breezer]

i asked the bg man about the "xnxjshgf wax valve thingy whats it" mine has that instead of a diverter, he says it detects the temp diffference and then operates letting water go to the taps

 

[karlos]

masona:

as i understand it there are 4 basic combi designs. i believe that two work with a pump on the HW side and the other two don't.

 

[dave18]

There seems to be some confusion on how the potty pumas work.

I will try & keep it as simple as possible. but pay attention I will test you on it tomorrow

1, there is only one heat exchanger unit but divided into two. So there are 4 pipes. flow and return pipes for the domestic hot water and a flow and return for the radiator heating.

2, When a hot water tap is turned on the mains cold water flows through the DHW part of the heat exchanger, and it works much the same as a multi point water heater. (the water being heated direct by the flames.)

3, But to confuse the issue the part of the heat exchanger that heats the radiator water is also getting hot. The diverter valve is positioned so that this water cannot get to the radiators but circulates round to the heat exchanger and so helps heat the domestic hot water and stops the water in this short circle from boiling.

This is why I said in my response to Breezer's problem that the hot water will work with out the pump running.

4, When the heating is turned on (no hot water to taps) the burners light the pump passes the hot water over the wax which allows the diverter valve to open and so the water is pumped round the radiator circuit.

5, At the same time the heat exchanger for the domestic hot water is also getting hot but as the water for the radiators goes past in the heat exchanger it cools down the trapped domestic hot water.

6, If you go back to Breezers post where he described the light up sequence. it happens like this because of the following:

Turn on a tap (no heating) and both heat exchangers get hot.

Turn off the tap and turn on the heating. the boiler fires and goes out this is because the water in the heating system is already hot so the boiler cuts out until the water has circulated and cooled down the heat exchanger and then the boiler re lights.

7, If you go the other way, the heating is on and you then turn on a tap you will notice you get some scolding water from the tap then it goes cold, and then slowly heats up as you would expect it to.

this is because the trapped water in the DHW side of the heat exchanger comes out of the tap first.

I hope the above makes sense, as I said in my previous post I was not going to write a book about it but it appears that I have

 

[breezer]

thats actually quite interesting, also explains why the hot water is hot, warm then hot, i didn't know that.

I for one would like to say thanks for that.