Hot water only available when central heating is on

[neverdated]

Hi

I have a Baxi Solo 2 40 PF boiler with a Danfoss FP715 programmer.

My problem is that the boiler does not fire up if the programmer requests hot water alone. In order to get hot water I have to have the central heating on as well.

Though the fault was unlikely to be with the original Wickes programmer, the unit was replaced in summer 2005 with the FP715.

The problem has existed for at least 10 months and this is the only change that has been made. I am unsure of the age of the boiler.



Have been reading this forum for some time now but this is my first post. Really hoping someone can help me out!

Thanks
Mark

 

[kevplumb]

check the switches on the back of the programmer are not set for gravity

FP715 two-channel full programmer

Item Number(s): FP715
The new look FP715 has a slimmer more modern enclosure with larger LCD incorporating a convenient backlight.

The FP715 two-channel full programmer has separate Heating and Hot Water outputs operating on completely independent time bases for maximum flexibility.
The FP715 can be configured by the installer at time of installation to provide 7 day, 24 hour, or 5 day/2 day operation and to provide either 2 ON/OFF's or 3 ON/OFF's per day, allowing the time control to be tailored to match the specific requirement of the consumer.

Additionally the programmer can be set for either 'pumped' or 'gravity' hot water.

The wallplate used follows the industry standard pattern, as used by many of the other time control manufacturers. This allows for direct replacement often without the need for re-wiring.

 

[neverdated]

check the switches on the back of the programmer are not set for gravity

Thanks for the response. I checked and double checked the dip switches when I installed the unit and it's definitely set to pumped. Any other ideas?

Thanks
Mark

 

[weareleeds]

Is it wired up correctly
live is obviously live
ditto for neutral
terminal 1 is dhw off
terminal 2 is htg off
terminal 3 is dhw on
terminal 4 is htg on

 

[neverdated]

Is it wired up correctly
live is obviously live
ditto for neutral
terminal 1 is dhw off
terminal 2 is htg off
terminal 3 is dhw on
terminal 4 is htg on

I haven't touched the wiring since moving to the property although it's possible that it was incorrect beforehand. I have taken a look but only as far as checking that wires are connected to the appropriate terminals. Any further work is beyond my level of competence.

If it's assumed that the wiring is OK, is there anything else that could be causing this problem?

If I get someone in to diagnose the problem, what should the approximate cost be?

And finally, what would the approximate cost be for an annual service of my Baxi Solo 2?

Thanks
Mark

 

[ChrisR]

Do you have a motorised valve (or two)? Look for a T junction of pipes which go into a brass thing which has a plastic or metal box on top.

Now I wonder how many plumbers are thinking "it couldn't be that because....."
But it could. You could have a faulty microswitch on a normal valve or a motor-open motor-closed valve.

 

[pjc]

A couple of questions:

-Does the boiler switch on at all or does it switch on but not fire up?

-Do you have a hot water cylinder thermostat fitted to your system?

Basically, some combinations of programmer and boiler will not switch the boiler on for hot water only, unless a cylinder thermostat is wired into the programmer. I had a similar problem recently. However, if the boiler switches on, but simply will not fire up, this may not be the problem.

If this might be the problem, the thermostats are about £10 and simply attach to the outside of the hot water cylinder.

 

[neverdated]

Do you have a motorised valve (or two)? Look for a T junction of pipes which go into a brass thing which has a plastic or metal box on top. You could have a faulty microswitch on a normal valve or a motor-open motor-closed valve.

Thanks for the suggestion.

Yes, I have two motorised values. If these were faulty could that result the boiler not switching on? I tried again with both valves manually open and it made no difference.

Cheers
Mark

 

[neverdated]

Does the boiler switch on at all or does it switch on but not fire up?

The boiler doesn't switch on at all.

Do you have a hot water cylinder thermostat fitted to your system?

Basically, some combinations of programmer and boiler will not switch the boiler on for hot water only, unless a cylinder thermostat is wired into the programmer. I had a similar problem recently. However, if the boiler switches on, but simply will not fire up, this may not be the problem.

If this might be the problem, the thermostats are about £10 and simply attach to the outside of the hot water cylinder.

Yes I do have a hot water cylinder thermostat fitted. When I fitted the new programmer last year it was suggested that the cylinder thermostat may be faulty. I tested this by removing it and touching the contacts together but it didn't seem to make any difference.

Thanks for the tips pjc, it's appreciated.

Maybe the problem is just the wiring between the programmer and boiler. Is there an easy way to test this? I am pretty competent at general household wiring.

Thanks again.

Cheers
Mark

 

[Gasguru]

It appears you have the standard S plan setup ie two motorised valves each controls by the timeclock and thermostats.

The microswitch in the hot water valve may have failed, the valve motor has partially failed or the valve spindle is sticking.

The timeclock puts 240V through the thermostat to power the valve motor. When the motor fully opens the valve it closes a switch, this switch then powers the boiler.

 

[neverdated]

The microswitch in the hot water valve may have failed, the valve motor has partially failed or the valve spindle is sticking.

The timeclock puts 240V through the thermostat to power the valve motor. When the motor fully opens the valve it closes a switch, this switch then powers the boiler.

Is there an easy way to test this?

Thanks for the tip.

Cheers
Mark