Auto Bypass Valve Stuck Open?

[davidm_uk]

In the recent cold weather my CH hasn't been able to get the house up beyond 19 degrees, so I turned up the temperature control on the boiler up from about 70% max to about 85% max. Sometime during the night the boiler locked out with an overheat fault. Reset it, turned the temp down a smidge, and turned the pump up from setting 1 to 2. Boiler hasn't locked up since, but house barely up to 20 degrees. All rads a quite warm (no cold spots so don't need bleeding), but not very hot. The system was balanced when I had a new boiler installed 8 years ago ( Worcester Bosch Greenstar 24Ri, new pump, new pipework and Honeywell DU145 Bypass valve). The CH and HW zone valves are operating ok, TRVs all fully open.

In poking about I noticed that the boiler out and return pipes were about the same temp, as was the pipe either side of the bypass valve (IR thermometer, black tape on pipes).

The bypass valve is set to just under 1, as done by the guy who installed the system. I'm thinking that maybe that valve has stuck part open, hence the return temp to the boiler being too high.

I've run the system up from cold, and the output pipe from the valve pretty much tracks the temp of the boiler output (lagged a degree or so, but probably the drop across the pump and pipes).

What do you guys think, I've read of a few bad reports on these DU145 bypass valves. Anything else you think I should try or test? Can give more details of system if needed.

 

[Mottie]

I had a similar problem on my system when it was converted to a sealed system with an unvented cylinder. I cured it myself by closing the bypass off, running it up to temperature and then slowly loosening the bypass valve until I could feel the hot water going through the bypass. I then tightened it back up half a turn. I assumed that I shouldn’t have anything going through that bypass when either 2 port valve is open. I had my pump on number 3, the fastest speed so that when both valves were closed there was enough pressure to open the valve. Been working fine since that.

 

[davidm_uk]

So was it the same make/model of bypass valve (Honeywell DU145), if so which direction do you turn it to close it off, is 1 off or 6? Logically it would be clockwise to turn off, like most valves and taps but......

 

[Mottie]

Don’t know what make. Just took a picture.

On my one, you screw it in clockwise to shut it off. If you do it when it’s cooled down, run the heating till the pipes are hot, you can soon tell when it’s opened as the bypass gets hot as you unscrew it. My one needed almost shutting right off then cracking open a bit.

 

[davidm_uk]

Thanks Motman. Anyone with a Honeywell DU145 Bypass valve can tell me which direction to turn the valve to shut/open it. At the moment setting it to 1 or 6 seems to make no difference to the temperature drop across it, hence thinking it's stuck open. I'm guessing that adjusting it is just compressing or releasing a spring inside that changes the pressure at which it should open.

 

[D_Hailsham]

It should be shut when set to 6.

Have you checked that it is the correct way round - the arrow should point away from the pump?

The pipe on exit side should be cold when valve is off. Leave several minutes before checking, then check as far from the valve as possible or you will just fell the heat conducted by the metal.

 

[davidm_uk]

Thanks for that. Yes, it's the right way round. I think I'll wait for this cold weather to warm up a bit before I turn the heating off to let things get cold and do that check, or I'll get angst from the Mrs!

 

[D_Hailsham]

Shutting the ABV for half an hour should be long enough to check if it actually works, i.e. exit pipe goes cold.

 

[Mottie]

Thanks for that. Yes, it's the right way round. I think I'll wait for this cold weather to warm up a bit before I turn the heating off to let things get cold and do that check, or I'll get angst from the Mrs!

No need to turn anything off - just turn the roomstat down for half an hour or so to let things cool down, fully close the valve then wack it up to say, three degrees higher than you usually have it to let it heat up then when its good and hot, s l o w l y open the valve bit by bit until bypass gets hot, tighten back up half a turn and that should be near enogh.

 

[davidm_uk]

OK, done that this morning. Exit pipe from ABV is getting as hot as input pipe (measured about 12" either side of valve) pretty much straight away. So looks like the ABV is stuck at least partly open. I assume that there are suppliers of ABVs other than Honeywell (hopefully with the same dimensions/connections) - any recommendations?

 

[Mottie]

So, it was getting hot straight away with the valve fully closed? Screwed right in like when you turn a tap off? If so, that looks like it’s the valve. I would imagine any plumbers merchants can supply a valve of the same dimensions for you.

 

[davidm_uk]

So, it was getting hot straight away with the valve fully closed? Screwed right in like when you turn a tap off? If so, that looks like it’s the valve. I would imagine any plumbers merchants can supply a valve of the same dimensions for you.

Yes and yes. I'l wait until the weather warms up a bit before doing it, will need a partial draindown of the system anyway.
Thanks for your help.

 

[robbob1980]

Hi. Did you get your abv replaced? I have the same DU145 and I think mine is stuck open too i.e. return pipe from abv starts to get hot straight away after turning the heating on. When I try to close the valve it seems to just keep turning. It was set at 5 and a half but it’s now at 6 and it’s no different.

Rob

 

[davidm_uk]

Rob - I'm still waiting for the weather to warm up(!) before I drain my system to replace the valve. The adjusting knob does turn multiple times, not just one revolution, there's a crafty plastic gear arrangement inside the knob - it all pinged out when I undid the locking screw too far. Don't turn it much beyound 6, the instructions say it can be damaged if you do.

 

[robbob1980]

Yeah I know what you mean about the weather. I don’t want to risk it either really.
I turned it a bit passed 6. Maybe to what would be 7 then thought better of it and turned it back. I don’t think my system even needs an abv, as my boiler doesn’t have overrun, and I have a rad with no trv in the hall where the thermostat is. I don’t know what would happen though if I keep turning it a lot passed 6. Will it close completely eventually? I’m pretty sure it’s faulty anyway so might give it a go.