Short cycling 2 boilers with P/S

Chad Brickley

I have two boilers, P/S controlled wiht Tekmar 262, primary DHW. I several firing issues. First, when a call for heat and the primary pump is on, the boiler fires and shuts down, fires and shuts down, etc.. never reaching high end of temp. Second, when the DHW calls for heat, both boilers are to fire but they fire, shut down, etc..... Any help to keep from short cycling and maintain longer boiler fire times? Is it all control based? Any input is greatly appreciated. Chad

The Kid

Chad had a some what of a similiar expereince with a problem your discribing. I found that the DHW aquastat in this case was shorting inside. I disconnected power and checked with my ohms meter...ohms conrtol bouncing.. problem fixed. lucky find..

S Davis

Boilers

What type of boilers are you using, and do they reach a set temp each time they shut down or is it random?
Pictures of the piping would also be helpfull.
Are you controlling the boiler pumps with external relays on each boiler?

S Davis


Apex Radiant Heating

Jay_12

P/S Boilers short cycling

Boilers piped in primary-secondary require the pumps on each boiler to purge after the burner has shut down. Otherwise the heat is trapped in the boiler.
I am assuming the boiler pump currently shuts off along with the burner. A drop out time delay relay on the boiler pump keeps the pump running after the burner has shut off and allows for boiler purging. This should correct your short cycling issues.
If you have any further questions, please call us at tekmar 250-545-7749.
Jay

Unknown

pipe diagram?

Chad,

Can you post (or e-mail me) a piping diagram?

wheels

hydronicsmike

AND...

...provide Mechanical Sketch

Chad Brickley

Reply

Gentlemen, Thank you for the input. A few answers... I have two 100,000Btu Dunkirk boilers. The current situation during the summer, when a DHW call, the control turns on both boilers and pumps. The boiler is firing, runs for 20-30 secs, shuts off and starts all over. The boilers do not reach maximum temp. The control still sends signal and pumps continue despite boiler on or off. On a side note, one of the boilers is not firing for whatever reason, and this is not the first problem with these boilers, on my sixth ignitor in two years, and now I believe the boiler control panel is not working according to the troubleshoot guide. Anyway, the boiler that is not firing, the pump is on until DHW demand has been met. I have enclosed a copy of the piping diagram and a few pictures. Thank you for the input.