I need to add an ABV but there is no easy access to a return pipe, is it acceptable to bypass to the top of the coil (indirect cylinder) creating the bypass loop via the cylinder coil to the return?
Auto Bypass Valve - Use top of indirect cylinder coil as the return?
- Thread starter woodpeckerx
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Yes, so long as the flow to ABV comes off before any motorised valves.
Thanks, its an S plan system so was going add a tee between the pump and HW valve and then another tee the other side of the HW valve into the top of the coil for the return as I cannot easily get to the return / bottom of the coil.
The bypass would basically create a loop across the HW valve.
The bypass would basically create a loop across the HW valve.
if your HW Cylinder is unvented absolutely no
That would mean that when there is a flow through the ABV, the HW cylinder gets primary flow, even if the stat is satisfied and the motorised valve closed, so gets hotter. Doesn't sound ideal. But why do you need an ABV? Can the CH side close down completely, eg all TRVs? Depends on what system you have.
Cyinder is vented
I know its not ideal but its going to be difficult to get to a return.
The reason for adding an ABV is the boiler has a frost stat fitted to the pipework next to it, in the winter the frost stat was calling demand from the boiler but the valves were closed, on quite a few occasions in the middle of the night there were tremendous banging noises like someone hammering hell out of the pipes, presumably becuase the frost stat kicked in but there was no loop for any flow.
The boiler also has pump overrun, so I assume the pump continues but both valves could be shut?
OK see what you mean, I can understand the banging, been there. Practically, your plan sounds OK to me. If the frost-stat calls, it's likely to be for a short time, so raised HW temp not a big problem. During pump overrun the boiler isn't firing so that's OK. Whether it's against any rules I don't know.
I suppose you can't tap in anywhere after the pump, before the valves, and pipe from the ABV to the boiler return?
unlikely that is a frost stat, most likely a pipe stat, that is fitted in conjunction with an actual frost stat, post pics of what you have and we will advise you better
It is a pipe stat, I just call it a frost stat. I still need to fit an ABV as if too many TRVs close the boiler gives an F26 poor circulation error.
I'm going to just bite the bullet and tee the ABV into the HW return.
That is the problem with asking for help online, you need to actually say what you have , not what you think, yes T into the HW return will work
Thinking about this again - the frost-stat (or pipestat) should be wired in parallel with the roomstat, so if it's calling, the CH valve opens (and fires the boiler via the microswitch). Otherwise the rest of the house isn't protected. And an ordinary frost-stat (not pipestat) must be sited where it sees the rising temperature from the CH, or the boiler will fire until the weather warms up!
In that case the only time the pump is against a closed valve is during overrun, and at least the boiler has stopped firing then. Though not ideal because the point of overrun is to dissipate residual heat from the boiler, which needs a flow.
The pipe stat in question is mounted near the boiler on the 28mm pipe in a single brick skin old utility room which gets pretty cold. It appears to be a very basic normally open switch, clamped onto the pipe with no temp adjustment. When cold the switch closes and demands heat using the switched live, as far as I'm aware the boiler will also start the pump but the valves won't open.
I'm also getting a low flow error from the boiler if I test with just 1 TRV open and a towel rail with no TRV so I think the ABV is needed anyway.
System is drained now and I'm half way through fitting it, connecting it on the return after the HW balancing gate valve at the bottom of the cylinder, was a pain to sweat off the old elbow due to no space but its off now and just putting the new 22mm pipework in.
I'm also getting a low flow error from the boiler if I test with just 1 TRV open and a towel rail with no TRV so I think the ABV is needed anyway.
System is drained now and I'm half way through fitting it, connecting it on the return after the HW balancing gate valve at the bottom of the cylinder, was a pain to sweat off the old elbow due to no space but its off now and just putting the new 22mm pipework in.
As I said, with that set-up the boiler is protected but the rest of the house is still at risk of frost. I think an ordinary frost-stat would be better, wired in parallel. In the utility room if there's enough heat loss from boiler and pipes to affect it, otherwise somewhere else in the house, but that might be difficult to get wires to it.
Sounds like it. Also deals with the pump overrun issue.