Baxi 105 HE combi boiler question

[VEEMAN]

Can any one answer the following question on the above boilers pump.
I noticed recently that the over run period seems to be getting constant pump switched on.
The HW runs fine and heats water no problem. The problem seems to be with the CH side.
The boiler fires o.k, pump cuts in, boiler goes up to room stats temp, boiler cuts off and pump over runs. After about 2 mins the boilers temp leds indicate 60 degrees and boiler fires back up again. The pump is running constantly and never switches off. So is this a feature of this type of boiler?
I've also noticed that the pump housing is getting very hot. Pressure on the guage is approximatley just over 1 bar when CH is running. I noticed that this has dropped down from 1,5 bar when the system was first installed 3 years ago.
Any advice would be appreciated .
Cheers
Veeman

 

[gas4you]

If the pressure has only dropped 0.5 bar in 3 years you are doing very well

I take it then it hasn't been serviced and topped up since new then

 

[namsag]

Yes this is normal and if you have water passing through pump at up to 80 degrees you should expect housing to get hot.

 

[VEEMAN]

I've kept an eye on the pressure over the past 3 years, and have topped the boiler up to the 1 bar when required.
So is this feature of the pump running constantly when the CH is in use?
It can not be very efficient if the pump is running all the time and the boiler is firing up every 2 to 3 mins. It seems to defeat the object of a constant air temp, it just seems as it gets hotter and hotter in the house. So what the use of the stat ect as the boiler does not seem to do it's job.
Cheers
Veeman

 

[Agile]

The boiler is doing its job perfectly!

If there is any problem its that you do not have a room stat or the settings are inconsistant or the rads are undersized.

Its not an "over run" its that there is a call for heat from the thermostat and the boiler fires up to provide that heat and as soon as the flow is up to temperature the burner goes out. All quite normal if the gas valve is set up properly and the heat load small!

Of course if I was setting it up then I would be setting the maximum CH power output on the PCB to ensure longer and quieter burner operation. However that is not a DIY setting and not even covered in the MI.

Tony

 

[VEEMAN]

Tony there is a room stat fitted. Today I removed the room stat conections from the boiler and replaced the link back in to the wiring loom. Boiler now set up with no stat to eliminate it. working off the boiler controls, boiler fired up, pump ran, heated up to 70 degrees so water reached desired set temp, boiler shut down, pump kept going. Temp reading on led reached 60 degrees boiler fired up.
This is working correctly as you say, but can you give me a straight answer to the pump runs on after requested heat is reached. Pump still runs ( to stop heat sxchanger boiling) reaches 60 degrees, pump shuts down, boiler waits for request to fire up again by stat or front boiler control settings.
I could be shot down in flames and I'm sure you can put me in the right direction.
Thanks for your answer it's appreciated
Cheers
Veeman

 

[Agile]

Its not an "over run" its that there is a call for heat from the thermostat and the boiler fires up to provide that heat and as soon as the flow is up to temperature the burner goes out. All quite normal if the gas valve is set up properly and the heat load small!

When the burner goes off the pump stays on to distribute the heat and monitor the temperature of the circulating water.

If it didn't do that it would not know when the rads had cooled to the point they need more heat!

Tony

 

[VEEMAN]

Thanks for the info once more Tony. Had a few questions fired at the guy who serviced the boiler today. Now sorted with the boiler and my doubt's that I had.
Anyway All the Best for 2008 and once more yuor help was appreciated.
Cheers
Veeman