Motorised Valve Auto Bypass

Hello Folks,

I've learnt a lot from trawling these forums over the years, I've diagnosed and replaced a faulty expansion vessel and zone valve recently thanks to you lot but this time I can't find the answer.

My mums boiler has a gate valve bypass directly underneath it. The boiler is a worcester bosch greenstar 30 cdi with an unvented hot water system. The problem I have is that because the boiler has so much latent heat in the heat exchanger when the heating and hot water cuts off, if you are running above 4 (1 to 6 available, 4 seems to be about 50-55C) then there is insufficient water in the bypass circuit to absorb it and it will reach boiling point, not good!

The current bypass is a 15mm gate valve directly under the boiler. What I would like to do is remove this and fit an auto bypass in parallel with either the heating or hot water motorised valve. That way the boiler can dump it's excess heat far more effectively so I can run it at a higher setting, it also means the heat won't go to waste like it does now.

So the question is, is there an obvious reason why this is a terrible idea? If I use the hot water tank to dump the excess heat at least it's stored and not wasted. I was also wondering if I am required to bypass any manual valves so it is impossible to valve off the bypass? This would mean fitting 2 bypasses in series with different pressure settings so that in the event someone stupidly closes something they shouldn't, it will still bypass properly. I'm presuming it's not a requirement since using a gate valve as a bypass inherently means the bypass can be manually valved off and this was acceptable, at least 8 years ago when it was fitted.

My other option is to simply extend the bypass pipework to add more water to the bypass circuit. Boiler is in the loft so space not an issue.

Cheers, Rich

 

Hi Slippy,
I appreciate that's where it normally goes, that's where the current gate valve is. But as I mentioned in my post the pipework in the bypass circuit doesn't contain enough water to use the boiler to its full potential. There is too much stored heat in the exchanger and it boils the water unless I keep it on a low setting. What I would like to know is are there any problems with what I propose? It might not be normal but it would be effective.

 

Excellent point on the cylinder. If the heating temp is set to 70C it would not be able to overheat the cyclinder I guess but still,big hot pressure vessel, lets not tempt fate.

So either use the heating valve and the rads or add more capacity to the bypass circuit. The same issue on the heating valve would just lead to a warm rads which is much easier to notice and not dangerous. Or I can get a 3m length of pipe and run it up and down the wall as part of the bypass, adding another 3.5 litres or so to the capacity of the bypass. Or do both and have different pressure settings for discrimination so it dumps heat into the rads unless some numpty has valved them off, then dumps it into the bypass.