rads red hot after flushing

[danlightbulb]

Hi,

Ferroli combi Optimax 31C. 7 rads + 1 towel rad.

We had our installer back out to flush our 6 month old system yesterday because the water was dark brown and rusty. I don't think he flushed it properly when he installed.

Since doing this most of the radiators are scorching hot. The towel rad is the hottest (untouchable) and nearest to boiler. The ones near the end of the pipe runs are hot enough too.

I tried to balance the system but I can't get a temperature drop. All rad valves were left full open by the installer. The LS valves are practically closed and i'm still seeing only 5 deg delta T. The combi is set to 80 degrees flow temp.

There also appears to be more flow noise now than before. There is also an occasional whistle from the boiler and there has been 2 occasions of loud banging too, like water hammer. I thought this may be air which should come out of the auto-vent on the boiler. I have bled all rads when cold and they are free of air.

I can't believe that a 6 month old system could have been so dirty that the flush made this much difference. Therefore could the installer have done something which I need to put right?

Many thanks

 

[superdupergasman]

The flow noise will be because you have all the valves shut down so much!

just leave the return lockshield half shut on every rad and if the rad temp is too hot for you turn it down on the boiler.

 

[D_Hailsham]

Since doing this most of the radiators are scorching hot. The towel rad is the hottest (untouchable) and nearest to boiler. The ones near the end of the pipe runs are hot enough too.

I tried to balance the system but I can't get a temperature drop. All rad valves were left full open by the installer. The LS valves are practically closed and i'm still seeing only 5 deg delta T. The combi is set to 80 degrees flow temp.

If you are running at 80°C with a 5°C drop, your boiler will rarely be condensing. Drop the temperature to 70°C for a start.

Open all valves (TRVs, manual and lockshields), get system up to 70°C and adjust pump speed to give a drop of about 15°C across the boiler.

Shut all lockshield valves, remove heads from TRVs and set manual valves to half open.

Open the lockshield nearest the pump about ¼ turn and adjust the drop across the rad to 15°C. Close the lockshield to increase the drop and vice versa. You should make very small adjustments, say ¼ turn or less. It will take several minutes for the temperature to stabilize. When the first rad is set, move on to the 2nd from the pump and so on.

 

[Agile]

Open all valves (TRVs, manual and lockshields), get system up to 70°C and adjust pump speed to give a drop of about 15°C across the boiler.

How exactly do you expect him to adjust the pump speed???

Even if he could, then it should be done with the lockshields in the balanced, mostly closed, position.

Tony

 

[D_Hailsham]

Open all valves (TRVs, manual and lockshields), get system up to 70°C and adjust pump speed to give a drop of about 15°C across the boiler.

How exactly do you expect him to adjust the pump speed???

OK, its a combi with an internal pump and the mfrs recommend speed 3 for max HW performance.

Even if he could, then it should be done with the lockshields in the balanced, mostly closed, position.

If that's how you prefer to do it, who am I to disagree?

The OP says he has a drop of 5 deg across the rads, but does not say what it is across the boiler. If it is also 5 deg, the pump speed is much too high as the drop is inversely proportional to the flow rate.

 

[Paul Barker]

Get an auto bypass fitted for starters.

 

[D_Hailsham]

Get an auto bypass fitted for starters.

The boiler has a built in auto bypass.

 

[simond]

Turn down the boiler stat, your rads may be oversized (no bad thing).

If you are only losing 5C across the rads then they are not discharging their heat into the house. As DH says, the flow rate could be an issue.

Was the property already warmed up when you are taking measurements?

Is there a room stat fitted?

Finally, I am not familiar with modern Ferrolis. We were a service agent, but I won't go there. Some boilers have a software configurable max output. Eg: You might have a 30kW CH boiler but it could have been set to 18kW before. My guess is that this was set lower and the installer has now cranked it up.

Water in a system does quickly discolour. I suggest that this problem may have been self inflicted. If you haven't got a new inhibitor dose you system will be in worse condition than before.