combi boiler hot water problem

[DP]

Boiler shutting down is indicative of heat not transfering to HW in HW mode. Eurocombi (I am sure) has cylindrical calorifier. With flowrate indicated, I would be looking for blockage on the primary side between the diverter and the inlet to the pump.

Is the plumbing plastic (if yes what is the colour of the pipes) or copper? What is water quality like when a radiator is vented.

 

[NScott1969]

1. Even at 12 ltr / min of hot water the boiler is still cycling.
2. The pipe runs are mainly plastic (white). Around the boiler the pipe runs are copper. The water quality is reasonably good.

Nathan.

 

[ChrisR]

Mechanism is that scale on primary side, or covering sensor(s) insulates so there's time delay between waters getting hot and the control system seeing it. Certainly the hw flow ate doesn't indicate that secondary side is constricted. The Proper test os to measure the temp drop across the heat exchanger(s). Mfrs provide the figs if you speak to them.

I'd also ask Ari what the effect of a deteriorating HW flow temp sensor would be - I'm not sure on this model. DP?

 

[DP]

I would take temperature reading on the flow pipe at the main heat exchanger. If possible, get two thermometers and post temperature on both flow and return connections of the main heat exchanger when boiler cuts out.

What temperature does the boiler thermometer indicate?

 

[derekh]

Have the same problem with my eurocombi SX20. When hotwater is demanded the boiler fires up and heats water up for a few seconds. The water heats up and is hot from the tap. Then the bolier turns itself off for a few seconds . The water temperature drops in the hot tap and the boiler fires up again and continues this process while there is a demand for hot water.(boiler keeps switching itself on and off continually...) The bolier appears to be operating at a max of 40C(according to the temp gauge).

I have recently descaled the bolier / central heating system with fernox system cleaner. The hotwater hot stopped working completely prior to this.

Another problem is it appears to be overheating (overheat stat pops out)when there is a demand for heating and the heating thermostat is set anywhere past half way.
Below this it appears to operate ok.

Any ideas anyone?

Cheers