Blockage in hot water circuit?

[garysz]

I believe that there is a floating blockage in the hot water circuit f my heating system. The system works for 5/10 mins then, when the blockage hits a narrow spot, the boiler sounds like it bolis the water and then turns itself off.

It has been there since we changed the three way valve last winter. I have drained the system three times, via a radiator, but it does not appear to find its way out.

Is there a drain point in the bolier?

Would a chemical additive remove it - I don't know what the blockage is made up of?

What would a plumber charge for seeing to it?

[Owain]

My /guess/ is that it's a piece of grit fouling the pump impeller. Ergo, when the pump stops, the grit is at the pump. Or some other intermittent fault with the pump.

Owain

[Aidan]

If it's broke after you've fixed it, you haven't fixed it.

I'd suggest that you check the wiring of the valve and ensure that it's the right motorized valve head; there are 2 different Honeywell types, at least. It may be that the 3-way valve is being closed by the thermostat, but that the boiler isn't being turned off as it should be. One of the 2 outlets of the valve should always be open, so this doesn't quite explain the problem, unless you've got the heating valved off.

The Honeywell wiring diagrams are available on their web-site.

[Harry Bloomfield]

garysz presented the following explanation :

Which will probably be the actual cause of 'the blockage'.

If the valve is not wired and the actuator properly located on the valve, then that might be 'the blockage'. Turn it on to provide hot water, then lift the actuator off the valve spindle, then try turning the valve by hand to the correct position. You should be able to hear when the water is flowing through and determine which circuit is being supplied with hot water by the pipes warming up.

[Owain]

I didn't :-)

[garysz]

The pump does not stop.

[garysz]

The 3 way valve was professional installed and works fine.

Interestingly the problem does not occur when both central heating and hot water are on - presumably less pressure throught a large circuit.

[Harry Bloomfield]

garysz formulated the question :

The problem IS the valve.