Baxi 105e pump runs constantly in CH mode

[Dutch85]

Could someone help me with the issue I have with my boiler please.

When in Central heating mode the boiler will fire up for a few minutes but the pump runs constantly - even with the dial on the lowest setting. Is this a characteristic of this boiler or a fault?

In my old house there was a worcester boiler and the pump would turn off after a few minutes or when you "clicked" back the dial.

This boiler doesn't have a room thermostat - I don't know if that would have an effect on the boiler constantly running?

Thank you

 

[D_Hailsham]

This boiler doesn't have a room thermostat - I don't know if that would have an effect on the boiler constantly running?

If there is no room stat, the boiler doesn't know if the house is up to temperature. All it can do is turn off when the boiler has reached the temperature set by the CH thermostat (left hand of the two rotary dials in the middle). The boiler is just cycling to keep the water at the set temperature (somewhere between 70C and 80C.) The pump therefore never stops as the boiler has not been told to stop by an external control.

A room stat will solve the problem.

 

[Dutch85]

Thanks for your reply. I've just downloaded a manual and it mentions that the pump should turn off.

3.1 Central Heating Mode (Fig. 2)
1. With a demand for heating, the pump circulates
water through the primary circuit. At a pre-
determined flow rate the central heating flow
switch operates, initiating the ignition sequence.
2. The main burner ignites at low rate, then the
gas valve controls the gas rate to maintain the
heating temperature measured by the
temperature sensor.
3. When the flow temperature exceeds the setting
temperature, a 3 minute delay occurs before the
burner relights automatically (anti-cycling). The
pump continues to run during this period.
4. When the demand is satisfied the burner is
extinguished and the pump continues to run for a
period of 30 seconds (Pump Overrun).

 

[ianmcd]

If there is no room stat, the boiler doesn't know if the house is up to temperature. All it can do is turn off when the boiler has reached the temperature set by the CH thermostat (left hand of the two rotary dials in the middle). The boiler is just cycling to keep the water at the set temperature (somewhere between 70C and 80C.) The pump therefore never stops as the boiler has not been told to stop by an external control.

A room stat will solve the problem.

No it wont

 

[Dutch85]

If there is no room stat, the boiler doesn't know if the house is up to temperature. All it can do is turn off when the boiler has reached the temperature set by the CH thermostat (left hand of the two rotary dials in the middle). The boiler is just cycling to keep the water at the set temperature (somewhere between 70C and 80C.) The pump therefore never stops as the boiler has not been told to stop by an external control.

A room stat will solve the problem.

Salus Wireless Thermostat, White, would it be a straight swap for the existing timer (mechanical type where you select the on off times by pushing tiny switches)? I've had a look and it has spade type connectors at the back. I don't want to do anything too complicated!

 

[D_Hailsham]

3.1 Central Heating Mode (Fig. 2)
1. With a demand for heating, the pump circulates water through the primary circuit. At a pre-determined flow rate the central heating flow switch operates, initiating the ignition sequence.
2. The main burner ignites at low rate, then the gas valve controls the gas rate to maintain the heating temperature measured by the temperature sensor.
3. When the flow temperature exceeds the setting temperature, a 3 minute delay occurs before the burner relights automatically (anti-cycling). The pump continues to run during this period.
4. When the demand is satisfied the burner is extinguished and the pump continues to run for a period of 30 seconds (Pump Overrun).

Referring to the numbered paragraphs above:

1. As there is no room stat there must be a permanent demand for heating. (Times determined by a time switch - if present.)

2. Not relevant.

3. This describes how the boiler's internal thermostat controls the water temperature. Note that the pump runs continuously during the ant-cycle time.

4. This state never occurs as the demand is never satisfied, so pump overrun never occurs.

The boiler is stuck in state 3: water heats up; reaches temperature set on boiler stat; boiler stops but pump continues; waiting time passes during which water temperature drops; boiler relights; cycle repeats.

 

[Dutch85]

Would the salus rt510bc thermostat be a straight swap? Just a case of swapping the spade connecters. Even though the numbers seem back to front on the salus thermostat compared to the mechanical timer I currently have?

 

[D_Hailsham]

Would the salus rt510bc thermostat be a straight swap? Just a case of swapping the spade connecters. Even though the numbers seem back to front on the salus thermostat compared to the mechanical timer I currently have?

Are you thinking of removing the existing timer and putting the wireless receiver in its place? If so, that will work but the wiring is a bit tricky as the connection in the boiler is designed for a timer only. The work has to be done by a Gas Safe Registered person as you the job means working inside the boiler casing, so it is classified as 'gas work'.

 

[ianmcd]

Doesnt matter what room thermostat you fit, if it is just the pump that is running and the boiler is not firing you have a boiler fault

 

[D_Hailsham]

Doesnt matter what room thermostat you fit, if it is just the pump that is running and the boiler is not firing you have a boiler fault

So the manual is wrong - "the pump continues to run during [anti-cycling]" ??

 

[ianmcd]

So the manual is wrong - "the pump continues to run during [anti-cycling]" ??

Of course it will run during anti-cycling, but it will not run continuously without the burner firing when a demand is present

 

[Dutch85]

Of course it will run during anti-cycling, but it will not run continuously without the burner firing when a demand is present

It does run continuously. Why would I say otherwise?

 

[ianmcd]

It does run continuously. Why would I say otherwise?

I never said that you did, if you read what I said, is that if it was an external control fault, this would ask the boiler to run constantly, so the pump would run and the boiler would keep firing up when the primary water temperature dropped, if it is only the pump that is running constantly and your radiators are not constantly hot then you have a boiler problem and fitting a room thermostat will not make any difference, but feel free to fit one and see who is correct

 

[D_Hailsham]

When in Central heating mode the boiler will fire up for a few minutes but the pump runs constantly - even with the dial on the lowest setting.

1. Does the boiler relight automatically after a few minutes?

2, What is the water temperature (a) normally, (b) on lowest setting?

 

[Dutch85]

1. Does the boiler relight automatically after a few minutes?

2, What is the water temperature (a) normally, (b) on lowest setting?

1 - yes it'll relight for a few minutes, then off, then back on etc

2 - no ideas on the water temperature. It's an analogue dial with no numbers on it.