I think in 20 years I have yet to find a Competently installed Alpha
Whats your point here? Is it that Alpha boilers need some sort of special installation techniques that confuse people, or the type of people that install Alphas are incompetent?
Pump in wrong place on Open Vent system...
- Thread starter littlepigeon
- Start date
Whats your point here? Is it that Alpha boilers need some sort of special installation techniques that confuse people, or the type of people that install Alphas are incompetent?
Hands up those on here who install Alphas! 
There is nothing special about Alpha boilers. However, they were cheap. And usually slung at the wall due to one or both parties being incompetent or tight.
Either get the fed and vent altered. Or relocate the pump to the boiler return.
Either get the fed and vent altered. Or relocate the pump to the boiler return.
Ok....pump location seems to be the one..... would you agree that this is the place the pump should be (green circle)? Ignore the return label on the pipe, that's actually hot water to taps... The pipe returning to the boiler is actually the white pipe running in the same direction to the right of it. Oh, and the picture doesn't show it very well but there is a manual bypass 15mm pipe that goes from flow to return for when both valves are shut.
Yes, but remember it needs to be controlled by the boiler.
Yup this is my main concern really due to locations of bothe the boiler and the vent/valves etc....
I don't think anyone has answered my wiring questions. maybe you could advise........Is it acceptable to run electrical cables externally? Obviously this would be miles better than tearing a few rooms apart to hide a new run of cable?
Cheers
Mains link RF
But the OP's CD24R has an output of 23.5kW and is designed for a differential of 20C. The boiler loss, which you estimate at 1m is nearer 2.5m at full output, assuming a 20C differential. This would rise to about 6m if an 11C differential is used. So your estimates are way out.
If the valve is open, even half a turn, it is acting as a bypass sending water straight back to the boiler without going through the rads or HW cylinder.
Where is the system bypass you mention - it's not shown on any diagram or visible in the pics?
Is it a automatic bypass and has it been set correctly?
Its a manual red turny handle type bypass, not automatic.
I watched a video yesterday that explained to just open it slightly, just to let a little water get through for when the valves arte shut down by the stats/clock. However, when both valves shut the boiler should stop firing, but there is the pump overrun to think about for a short while, so a little water needs to still get round. If i shut it completely this would be an issue surely?
Its on the sketch, its the little thin red pipe coming down to the fatter return pipe. It is also shown in the picture coming off left from the flow to the water valve, coming down to the return. You cant make out the pipe but i have drawn some red arrows on there showing its direction.
I watched a video yesterday that explained to just open it slightly, just to let a little water get through for when the valves arte shut down by the stats/clock. However, when both valves shut the boiler should stop firing, but there is the pump overrun to think about for a short while, so a little water needs to still get round. If i shut it completely this would be an issue surely?
Its on the sketch, its the little thin red pipe coming down to the fatter return pipe. It is also shown in the picture coming off left from the flow to the water valve, coming down to the return. You cant make out the pipe but i have drawn some red arrows on there showing its direction.
As I said, those estimates were based on my system. For 24kW and 20°C rise the water flow is just over 1m3/h, lower than my 1.15, so the pipe and rads loss is lower. Yes the boiler loss is higher than I used, so the pump differential is higher, but that doesn't affect the pressure rise at the vent connection, which is the main thing I was estimating. Also, as I acknowledged, my estimate of 1m at that point must be too high, as unless he has an unusually high vent pipe loop it would be pumping over continuously. Of course it's impossible to make accurate estimates without knowing more details of the system.
The Alpha instructions are a bit odd in that only one flow is used, which relates to 18kW. It doesn't say whether the same curve applies to all models, so to use higher flow/pressure drop for 24kW, or the h/ex size varies with boiler rating, when a different curve would apply for each. If the latter, the drop at design point, 20°C rise, might be similar to the 1.4m on the curve.
I got confused and thought that the bypass was something separate from the 15mm pipe with a gate valve on it. You should replace the gate valve with
an automatic bypass valve. At the moment hot water is continually going straight from the boiler flow to the return, which increases the return temperature. This reduces the ability of the boiler to condense.
The short parts list at the back of the installation manual shows one hex for the 13kW and 18kW, with a different hex for the 24kW version. So your surmise appears correct. Alpha should publish two curves, not one.
@littlepigeon ignore the physics boffs chatter. Just get the system layout configured correctly according to the advice given by the experienced tradesmen here and the MI's. It ain't rocket science, but shares some traits.