Replacing 3-way valve in wood-pellet boiler system

Hi Matt
Thanks for the reply. I'm not at the house at the moment but from memory the boiler is a Kunzel PL25, the store is also made by Kunzel and is 500L. Heating in the house is just by radiators. Not at house as I said so can't give piccies at the moment, but which bits in particular?
Cheers
Ben

Matt
Forgot to say, the pipework is all 28mm and copper. Changes to plastic running to house from just after the pump on C and from the T at D. There is a drain valve/tap on the pipework at the bottom of the thermal store.
Cheers
Ben

Hi Ben

Thanks for additional info. More pics of current boiler and pipe work from boiler to buffer would be good. No dis respect Ben but are you absolutely confident that you can carry out the work?

Is the heating and hot water controlled by motorised valves and thermostats?

I would recommend you replace the faulty mixing valve with a ESBE model. This will provide endless years of hassle free efficient use.

Make sure the boiler is completly shut down and has gone through its de ash cycle before you drain down. I would recommend you install full bore lever valves on all pipe work connections to the 500ltr buffer (but not the open vent pipe on top, if it is a vent pipe?). As to your drawing I would recommend the cold feed is reconfigured too (poor system design to be honest) or you should think about sealing the biomass and buffer system (pressurised). While the system is drained replace the pump valves with 28mm full bore perfect pump type this will provide better flow rate to the house system. As you have plastic pipe installed are you aware this is not allowed on biomss systems? I noticed there was no air separation device or system magnetic filter. Spirotech sell a dual air and dirt separator and you can purchase one with 28mm compression fittings. I would install temperature and pressure gauges in numerous positions on your system to help if you get any hydraulic problems.

Make sure you install the right amount of inhibitor when you re fill the system too.

Is there anything else I can help with?

Hi Matt

Many thanks for the advice - really helpful. Yes, heating and hot water controlled as you say. No disrespect taken at all - I feel pretty confident that I can drain down and change the three-way mixing valve (this is controlled by an automix controller) and cutting in the isolation valves seems straightforward enough. Any top tips though would be much appreciated. Don't think I would be confident reconfiguring beyond this as you suggest but will consider that in future (as we may make some changes to the system in the next two years or so anyway).

Thanks too for the other comments. We got the system installed c.8 or 9 years ago, and whilst it has run very well for all that time I do get the feeling in hindsight that it was a bit of a slapdash installation (despite them being an accredited installer!)

Cheers

Ben

Hi Ben

Thanks for the reply. Well I guess you know to isolate the feed and expansion cistern and then to drain the water at the systems lowest point (this will be at the bottom of the 500ltr buffer tank). If there are isolation valves on the flow and return pipe work to the house then these should be isolated too. Open any manual air vents on top of the buffer tank and boiler and keep the hose connected to the buffer tank drain off whilst you loosen the mixing valve compression nuts. Replace the mixing valve and cut in your new isolation valves to the buffer tank. You can always cut in isolation valves to each pipe feeding the mixing valve as this will prevent the need to drain down should the problem happen again. Very important they are full bore lever type designed for solid fuel or medium temperarture hot water applications and use high temperature sealing compound on each valve olive to help create a super tight seal. When you've completed those bits close all air vents and drain off valves and then open the isolation valve to the feed and expansion cistern. If your happy there are no leaks proceed to add inhibitor into the feed and expansion cistern. At this point you should contact the manufacturer to confirm what PH value the water should be going through the boiler and buffer. Re light the boiler and let it run for a couple of hours whilst this is happening you should be going round the system releasing any air from manual or automatic air points, especially the boiler charging pump and mixing valve circualtion pump (one in picture). All air MUST be released from the system!. Buy some Litmus papers from Amazon and check from numerous points on the system (radiator bleed points, buffer tank drain off etc) to confirm the correct PH value has been achieved. Check boiler parameters on boiler control liasing with the manufacturers instructions or with the manufacturers technical help line.

Job done!

Good luck and let us know how you get on.

Mech Matt

Hi Matt
Thanks for all the advice. I've installed the isolation valves and perfect pump valves and replaced the faulty 3-way valve - all seem fine. Filled up the system and fired up the boiler. Have not yet fed in inhibitor as only just done the job and wanted to check everything ok. Bled all rads and released air from water into hot-water cylinder and from hot water returns and from pumps.

BUT... when I put the CH on the rads are not getting warm. Well, one is getting a little warm but the rest aren't really doing anything. Assuming I have an airlock somewhere but a bit stumped to be honest -any ideas?

Ben

Ignore above - have managed to fix CH. Thanks again for all help

B