Old Ideal boiler with two pumps

[kinggeorge]

System is 30 year old and has two pumps one for central heating one for domestic hot water.

When the hot water tank gets very hot when the heating is switched on the bolier will not flame up but the pump runs.
The only way to get the heating on is to run away hot water until the bolier kicks in.

There is no divert valve that I can see only two separate pumps.

 

[stevetheplumber]

sounds like the wiring has been altered at some point
this system was common at one time and it is simple and effective one pump is fired by the cylinder stat and the other by the room stat bioler was usually fired from the hotwate demand from the clock and you couldnt run heating without hot water
a slightly more sophisticated sysytem had a relay which allowed hot water and heating to be used independantly
a anti gravity vale was normally fitted on the heating system to prevent creep

 

[kinggeorge]

Many thanks for the reply.
Once the water in the cylinder gets hot the central heating will not fire up unless water in considerable amounts is drawn off.

This would indicate I assume that the sensor which is held not in the tank to the tank is asking the bolier for hot water so the system fires up.

What makes the heating fire up the clock which is set on constant plus the wall thermostat which is on full.

I am baffled.

sounds like the wiring has been altered at some point
this system was common at one time and it is simple and effective one pump is fired by the cylinder stat and the other by the room stat bioler was usually fired from the hotwate demand from the clock and you couldnt run heating without hot water
a slightly more sophisticated sysytem had a relay which allowed hot water and heating to be used independantly
a anti gravity vale was normally fitted on the heating system to prevent creep

The central heating pump runs and stops when you move the wall thermostat up and down so that is working OK.
Turn the stat up the pump runs turn it down the pump stops.

What else tells the central heating to fire up.


hermostate

Many thanks for the reply.
Once the water in the cylinder gets hot the central heating will not fire up unless water in considerable amounts is drawn off.

This would indicate I assume that the sensor which is held not in the tank to the tank is asking the bolier for hot water so the system fires up.

What makes the heating fire up the clock which is set on constant plus the wall thermostat which is on full.

I am baffled.

 

[kinggeorge]

The only way the boiler now fires if the domestic water is left on constant is by running off hot water.
You can turn on the central heating and move the bolier setting to 6 the max but unless you run water off the bioler will not fire.

Many thanks for the reply.
Once the water in the cylinder gets hot the central heating will not fire up unless water in considerable amounts is drawn off.

This would indicate I assume that the sensor which is held not in the tank to the tank is asking the bolier for hot water so the system fires up.

What makes the heating fire up the clock which is set on constant plus the wall thermostat which is on full.

I am baffled.




The central heating pump runs and stops when you move the wall thermostat up and down so that is working OK.
Turn the stat up the pump runs turn it down the pump stops.

What else tells the central heating to fire up.


hermostate

 

[Dal5band]

Hello Kinggeorge - don't know if you solved your problem of two pumps etc. I have a very similar system which i have modified.

The original system worked by having the boiler "on" all the time the HW clock signal was on. HW thermostat runs the HW pump, the CH thermostat runs the CH pump whenever each needs heat but the boiler stays on regardless - this causes the boiler to recycle when both thermostats are satisfied.
In your case someone has wired the boiler to only come on when the HW thermostat calls for heat - this is OK for summer use as the HW thermostat directly controls the boiler.
You could improve this by fitting a Summer/winter switch. Just an on/off switch that switches the HW on clock signal to the boiler so the boiler stays on all the time. The CH pump can then draw on the heat from the boiler. In fact there may already be such a switch. Incidently, the HW may get too hot by gravity feed through the HW pump depending on the pipe runs..

My modification is a much more complex job and involves using a relay so either pump can turn on the boiler. You need a relay so the "other" pump does not come on when not required. If you just wired both pumps to the boiler (without a relay) they would be inter-connected electrically - not good.