Vaillant 630 and tellford cylinder

[grant lyons]

Apologies for the silly questions in advance.
I have a vaillant 630 plus system boiler tied to a 300l Telford cylinder.

The entire house is heated by UFH with manifolds on each of the 4 floors and each room having a thermostat.

The heating and hot water go through the cylinder which is heated by the boiler.

The cylinder itself has a stat which is connected to an backup immersion element, none of this is connected to the boiler. Both the cylinder thermostat and boiler are set to 65 degrees.

I assume the boiler fires based on the return temperature coming from the cylinder? Is it better or does it make any difference to install a cylinder stat to connect to the boiler.

enormously grateful for any insights before getting a new cylinder fitted!

 

[Johntheo5]

Have you got a Thermal Store?.
Is the DHW heated by means of a coil in the thermal store?.
Why do you require a new cylinder/TS?

 

[grant lyons]

Both DHW and UFH are heated by the cylinder so does that make it a thermal store?

I have flow and return for the boiler, flow and return for DWH and obviously hot water draw and cold water inlet.

I had the cylinder installed in 2007 and am replacing as the immersion element has been weeping for years causing quite a bit or corrosion and as we are moving abroad for a few years and renting the property I think it’s best to replace.

 

[Johntheo5]

Both the cylinder thermostat and boiler are set to 65 degrees.

I assume the boiler fires based on the return temperature coming from the cylinder?

Yes, it is a thermal store.
You say above that both the cylinderstat and the boiler stat are set to 65C, and then say

Is it better or does it make any difference to install a cylinder stat to connect to the boiler.

not sure what you mean as the cylinderstat should switch the boiler on/off anyway.
I think the cylinderstat will be located low down ( near the boiler return) so would think that the boilerstat should be set considerably higher, say maybe 75C/80C because there will be a temperature rise (dT) through the boiler, normally 10C to ~ 15C, so if the cylinderstat switches in the boiler at say 60C then the boiler will definitely cycle constantly if its setpoint is only 65C. Are you experiencing this?.

 

[ianmcd]

Pictures tell a thousand words , show us what you actually have

 

[grant lyons]

Have you got a Thermal Store?.
Is the DHW heated by means of a coil in the thermal store?.
Why do you require a new cylinder/TS?

 

[grant lyons]

The boiler is not connected to the cylinder currently.

The cylinder does have a stat as the attached image shows but this is not connected to the boiler.

The boiler currently has a 230v flex cable and no other electrical connections or wires.

 

[Johntheo5]

What is the boiler heating??, is the electric immersion heating the cylinder?

 

[grant lyons]

The boiler heats the cylinder. The immersion heater is only for backup and is usually switched off

 

[Johntheo5]

So what tells the boiler to fire, there must be a stat in the cylinder to do so, with no stat and say the boiler is programmed on then it will keep heating the cylinder until the boiler stat switches it off, say at 75C, the cylinder then cools down but the boiler may stay hot for ages so won't fire up again?.

I think I know what it does. it keeps the boiler circ pump on "permanently", circulating from the cylinder bottom, to the top.