Pump overrun problem with hot water only.

[inahole]

I had my basic gas heating system reworked professionally and a new boiler (Glowworm Ultimate ) and an electronic programmer/ timer installed. The system functions after a fashion but I have noticed that while the central heating work as expected, the hot water does not.

The heating operates according to the programmer, responds to the room thermostat and fires up the boiler and pump, which turn off once the thermostat setting is reached, with virtually no pump over-run. The hot water, however, when operating on its own will respond to the tank thermostat, firing up boiler and pump, but once the boiler has finished burning the pump runs on - not just for a few minutes, but for up to an hour. Although it does vary as to how long , it does eventually turn off. It has on occasions also some on outside its programmed hours when the controller shows water as OFF!

I contacted the programmer manufacturers who said the problem was with the boiler as it controls the pump in order to protect itself from over-heating. I cannot see that it could be the over-run thermostat as it appears to operate correctly when the heating alone is on.

My suspicion is that something is incorrectly wired but no-one seems interested in taking on the problem - any ideas welcome!

 

[corgiman]

Its perfectly ok as its temperature controll and will keep running until the temp in the return has been lowered enough.

The water in the flow and return will get hotter whenthe system is just heating up the hot water as there is very liitle surface area to sink the temp via radiationm this is not a prob the the CH mode cos off all those rads

 

[inahole]

Thanks for this response which goes some way to explain the over-run situation: Two points:

1. This implies that my water temerature when operating without CH is governed by the over-run thermostat, and at present it must heat up to the tank thermostat setting - about 55 degrees - then get circulated around the primary system until it is lowered to the (unknown) boiler setting - very inefficient! I might as well reduce the setting on the tank stat - although its not high already.

2. It does not explain the boiler firing for hot water when the controller shows it to be OFF.