Boiler bypass valve

john-306

Hi, I've got a glowworm boiler that because of the cold weather has started to activate the external frost stat overnight, once the boiler starts up the temperature quickly rises then shuts off with a F5 error.
The boiler works perfectly at other times, it's only once frost stat activates that the error occurs.
I've manually activated the frost stat and the boiler fires up, pump starts then temperature quickly rises then shuts off.
There is a taconova setter 15mm valve used as a bypass, could it be a problem with this, do these tend to fail?
I've searched for new ones but only used from ebay are available, doesn't seem to be any 15mm bypass available these days. Any options if this is the problem, or any other ideas?
Many thanks.

fezster

You could have an Automatic Bypass Valve installed (ABV):

https://www.screwfix.com/p/honeywell-straight-auto-bypass-valve-22mm/34127

If you have a smart pump being used in Proportional Pressure mode, though, the Taco setter is recommended. It may just need adjusting to allow more flow through it. The boiler is not able to dissipate the heat fast enough with the zone valves closed.

john-306

Thanks fezster, cant see anything installed in the airing cupboard where all the pipework and pump etc is installed.
I'm assuming the Taconova is being usad as a bypass when the frost stat kicks in but isn't working so causing the F5 problem

fezster

Your boiler manual will show the minimum flow rate required. The Tacanova setter needs to be adjusted accordingly. However, I believe it constantly bypasses, whereas an ABV kicks in only when the differential pressure is high enough to open it.

john-306

With both the rad and cylinder valves closed when the frost stat kicks in, the boiler makes a right racket then temp rises and it shuts off with F5, I'm assuming it should go through bypass and continue running, but it doesn't so again I'm assuming the Taconova is somehow faulty, it looks really old and the display is faded, I've no idea what it should be set on.
Any advice, thanks.

Alex1983

Is it the bypass with a flat head screw slot and window to see in with numbers on, if so the 15mm version is a fixed bypass with a rate of 3-12l per minute.

As fezster has said you need to look at the manufacturer instructions and see what it says the minimum flow rate is and you can set it accordingly.

Alex1983

Is it the bypass with a flat head screw slot and window to see in with numbers on, if so the 15mm version is a fixed bypass with a rate of 3-12l per minute.

As fezster has said you need to look at the manufacturer instructions and see what it says the minimum flow rate is and you can set it accordingly.

john-306

Alex1983 wrote: »

Is it the bypass with a flat head screw slot and window to see in with numbers on, if so the 15mm version is a fixed bypass with a rate of 3-12l per minute.

As fezster has said you need to look at the manufacturer instructions and see what it says the minimum flow rate is and you can set it accordingly.

Yes that's the one.
Minimum flow rate 773.8 litres/hr, but I can't make out the window setting as its discoloured apart from I think 4, 6, 8 10, 12.
It's got markings of 0, 2, 4, 6, 4, 2, 0. around the flat screw slot itself.
Is this likely to go faulty as 3 previous winters we have been at this house we've never had this problem?

MikeEngTech

Just because you have a bypass doesn’t mean the boiler will dissipate the heat.
Might need a longer bypass loop or a boiler with better modulation. They are mostly just to protect the pump. The taco setter is very good. Contact the installe if you can, sounds like he knows what he is doing. I would let the heat dissipate through the rads though. I wouldn’t have this type of control system.
If you search YouTube for “Ainsdale hasn’t Pump curves” you will find a video I did which explains different types of pump curves and bypasses including a mention of flow setter for proportional pressure or burner linked pumps. Very good advice in this thread already though.

MikeEngTech

“Ainsdale Gas pump curves” on YouTube I mean

john-306

MikeEngTech wrote: »

“Ainsdale Gas pump curves” on YouTube I mean

Thanks for the link, a little beyond me unfortunately.
I can't contact the installer as the previous occupants had it installed.
I've read once frost stat operates it only has to circulate to protect boiler and pipework at risk, there is no need to circulate around rads and heat up the house while sleeping.
What I'm not understanding is why when the central heating is on the inlet to the tacosetter is hot, the outlet is cold, even when tacosetter set to fully open, surely there should be some flow through it.Maybe thats why my boiler when frost stat kicks in it overheats and shuts down?