Worcesters in Tandem

[TonyP]

I have just installed a boiler sequencing control for my twin Worcesters connected in tandem. Oddly, I have discovered that when the RH boiler is the only one firing, hot water does not circulate; but when the LH boiler is the only one firing, water circulation is OK. When both are firing, ciculation is also OK. The electrics all seem to work perfectly, it must be a plumbing design fault but the installer denies it.
Basic design is that the two flow pipes come together at a T and then the water goes through the pump and around the system and returns through a common pipe to the two boilers. A second branch circulates DHW via a smaller pump and exhibits exactly the same problem but more obviously because of the smaller pump.
Any ideas? Could it be some sort of imbalance, should there be valves controlling flow from each boiler? Help??

 

[Plucky]

Can you get a pic at all? Have you checked operation of pump and that motorised valve is being energized?

What is this boiler sequencing you use? Ive installed several worcester boilers in tandem but the sparky wires em, I dont get involved. Im sure he just uses a series of relays, But i'd be interested to see if there is a specially designed product

 

[TonyP]

Hi,
Thanks for the quick reply! The sequencer was ready built by Warmworld (see Intelligent Central Heating Controls - Save money on heating bills). It was wired by a sparky and all the signs are that it works very well. The pumps and motorised valve work OK and when they should.
I drew a rough circuit diagram of the plumbing for Warmworld and have attached it for your interest.