Central Heating flow problem?

[Smouser]

Good afternoon,

We have a Glow Worm 24hxi boiler and two heating zones (downstairs and upstairs). When only the downstairs heating is turned on, the boiler fires up and the temperature displayed on the boiler rises quickly to about 50+ degrees and then the boiler 'ramps' down. The temperature on the boiler then rapidly goes down and the boiler ramps up gain. This ramping up/ramping down then repeats constantly.

However, if I have both heating zones turned on, it does not happen. The boiler fires up and the temperature displayed on the boiler's display is pretty steady at around ~ 47.

What I think is happening when only the downstairs zone is turned on - the water in the boiler gets warmed up but because it does not get pumped through quickly enough, the boiler ramps down. As soon as the boiler ramped down, the hot water was pumped away and the boiler ramps up again.


Background information: The system has been installed since 2008, I have never noticed the problem until this winter. The central heating system is pressurised. We have got a Grundfos pump, do they lose performance over time?

Help and advice are much appreciated.

 

[Terrywookfit]

Less load is less gas
What do you expect to happen.

 

[Smouser]

Less load is less gas
What do you expect to happen.

Maybe I have not explained it well enough, let me try again.

With only the downstairs heating on, the boiler fires and heats 'full blast' with the fan loud for a few seconds and then the water temperature on the boiler's display goes above 50 degrees. The boiler and fan then ramps down and the water temperature drops, immediately followed by the boiler and fan ramping up again and so the cycle repeats. The boiler is not working at a constant rate, it keeps cycling like that.

However, with both heating zones on, it works at a constant rate and does not do all this ramping up/ramping down stuff.

 

[terryplumb]

Is downstairs heating zone radiators ,underfloor heating , both ? Whatever it is ,does the heating function ok ?

 

[Smouser]

It is radiators downstairs. They do get warm but it takes a long time, I think it is because the boiler keeps ramping up and down and not constantly working.

 

[terryplumb]

If both zones are turned on at the same time ,do downstairs radiators heat up quicker ?

 

[Smouser]

I have not really checked/noticed. I will try to test that in the morning.