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I have a vented S Plan with a System Boiler stacked over the DHW Cylinder in a tight airing cupboard. The Cylinder is 1150 High and over it is a Vaillant Boiler. All is working perfectly with flow to a first floor shower just acceptable and we have plenty of stored hot water. But we are about to...

I experience the sudden shutdown as the temperature rise is quick. Usually when the system is only serving DHW and that is nearly up to temperature. So what pump setting and bypass will help this? If the bypass is mostly open and the pump is on the lower setting the water is returning with...

That's more understandable! So perhaps a variable speed pump can work with a 428.

But they are not disconnected. They appear to blend. But perhaps the LLH allows both sides to run at different flow rates although I don't see how the pump from one side won't interfere with the other? So in an ideal setup the boiler pump would be a single speed constant and the demand could be...

Having looked at the minimum flow rates for my 428 I can see a number of settings to get 20.3 litres per minute. I've settled on pump speed 2 which is a head of 3.5 metres with the Honeywell bypass set to 3.5 from their chart. But I could have selected a pump speed of 1 to give 2.5 metres of...

So it looks like I should open the Automatic Bypass AND set the pump to position 2. But I still can't get my head around the 'shortcut' that the bypass provides straight back to the boiler! The boiler is heating the water to 70c and a portion is going straight back in the return side with...

Interesting thought!

I'll measure the temperature drop with my meter but this afternoon it didn't seem to be much different on flow and return. The bypass is flowing with both Heating and DHW in use. If the heated water is going straight back to the boiler won't I have colder radiators and a boiler that is shutting...

I set it at 4 because it starts flowing almost as soon as the boiler fires up. I thought it was better to have it only opening when the valves shut down. If I open it won't the hot water just go back to the boiler quicker and shut it down? I was hoping that the variable speed pump would mean...

Honeywell bypass set to position 4

Eight radiators and it's S Plan Vented Cylinder (fairly new and well insulated). I tried it on Fixed Speed 3 but the pump noise is heard in the hall below. I've just reduced D0 to 12 (it was on 15) and set the fixed speed to position 2. I've left the target temperature at 70c. During the...

'Low Fire Mode' sounds like the experience I'm getting. I upped the boiler temperature to 70c and observed this. After the boiler fired it ran at probably max for 35 seconds and got to 60c before running very quietly. The flame symbol was on as it reduced down to 40c. Then with the flame symbol...

Do they work together? Part of sorting out the flow in my system was the fitting of a new pump. (The poor power flush filled the old one with iron filings but did cure the boiler noise). So I have a UPS2 which has the 'Variable Speed Mode'. The system is a conventional with loft supply tank and...

Wouldn't lack of water flow point to air rather than pumps or bypass? I suppose the pump not turning on might cause it.

Just looked up your boiler and it says it is 'Open Vent' ie a tank in the loft. Still lack of water is the primary fault for F83. After that it's the sensors measuring flow and return temperatures

Vaillant say this is insufficient temperature increase once the boiler is lit... Low System Water Pressure Flow Or Return NTC Thermistors Out Of Calibration (Should Read 12Kohms @ 20C) Or Not Connected To Pipework Correctly Damaged Or Loose Connections On The Wiring Loom Between The NTC...

The ABV runs from just below the flow side of the pump and joins back again at a tee for the CH return. It then flows through the tee for the DHW return and finally through the TF1 filter. But hardly anything is being trapped in the filter, just a fine dust. I'm glad to hear that I might be...

I think I probably have 2 or 3 mm of stuff on the pipe wall but the performance of all radiators is now excellent. If I stick a pipe brush through the bit I don't cut out will the dust left cause more problems?

Pity you're not closer to SW London. But would you brush out the visible pipes or allow the chemicals to do it?

So, if you can do it without magnets, how do you catch those bits coming out the boiler. I'm assuming the best place to connect is the pump valves and what I don't want is to push stuff into the other side of the boiler. Also, I've found a piece of pipe beyond the CH Valve that a magnet can...