Old wiring mess replacement for boiler

diggerdigger

Hi. Recently bought an old house that has 2 newish domestic baxi megaflo boilers chained together, which work fine, but ...

The wiring for the controls is a huge convoluted galvanized steel box with a mess of wires where incorrect old (black and red and blue and brown) have been comingled, coloured wired misused, with bits of tape added, and spaghettied.

So I have a feed from the main house fuse box, through a giant 60amp galvanised fuse switch, to a second big old galvanised steel fuse box, then on to a newish mini 2 fuse box which runs the wires back through the same big steel conduit to a timer (that cant switch off cause its mis-wired somewhere) and then on to the 2 circuit pumps and valves.

What i want to do is take it all out and scrap it, and put the feed from the house main fuse box to a 3amp fused switch an into wiring centre to 2 actuators to control the 2 zones.

Is there any issue putting 2 boilers, each with its own internal pump, 2 circuit pumps just behind a simple 3a fused switch?

Dardania

diggerdigger wrote: »

Hi. Recently bought an old house that has 2 newish domestic baxi megaflo boilers chained together, which work fine, but ...

The wiring for the controls is a huge convoluted galvanized steel box with a mess of wires where incorrect old (black and red and blue and brown) have been comingled, coloured wired misused, with bits of tape added, and spaghettied.

So I have a feed from the main house fuse box, through a giant 60amp galvanised fuse switch, to a second big old galvanised steel fuse box, then on to a newish mini 2 fuse box which runs the wires back through the same big steel conduit to a timer (that cant switch off cause its mis-wired somewhere) and then on to the 2 circuit pumps and valves.

What i want to do is take it all out and scrap it, and put the feed from the house main fuse box to a 3amp fused switch an into wiring centre to 2 actuators to control the 2 zones.

Is there any issue putting 2 boilers, each with its own internal pump, 2 circuit pumps just behind a simple 3a fused switch?

In principle no provided both the steady state and inrush current is okay for 3A fuse, however for maintenance purposes it might be better to have 2 fused spurs, one for each boiler.

What are the 2 boilers for - are they plumbed in parallel in order to meet load reasone, or for redundancy? Or is one dedicated to a particular zone? There may be a method to the madness on the wet side that should be considered on the electrical side.

Also, be aware that some boilers prefer continuous live with a separate enable signal, to allow them run on after **** down to dissipate heat, or they periodically run the pump to ensure it doesn’t seize.

Bruthal

diggerdigger wrote: »

Hi. Recently bought an old house that has 2 newish domestic baxi megaflo boilers chained together, which work fine, but ...

The wiring for the controls is a huge convoluted galvanized steel box with a mess of wires where incorrect old (black and red and blue and brown) have been comingled, coloured wired misused, with bits of tape added, and spaghettied.

So I have a feed from the main house fuse box, through a giant 60amp galvanised fuse switch, to a second big old galvanised steel fuse box, then on to a newish mini 2 fuse box which runs the wires back through the same big steel conduit to a timer (that cant switch off cause its mis-wired somewhere) and then on to the 2 circuit pumps and valves.

What i want to do is take it all out and scrap it, and put the feed from the house main fuse box to a 3amp fused switch an into wiring centre to 2 actuators to control the 2 zones.

Is there any issue putting 2 boilers, each with its own internal pump, 2 circuit pumps just behind a simple 3a fused switch?

You could put a 3A fused spur for each boiler.

diggerdigger

Dardania wrote: »

In principle no provided both the steady state and inrush current is okay for 3A fuse, however for maintenance purposes it might be better to have 2 fused spurs, one for each boiler.

What are the 2 boilers for - are they plumbed in parallel in order to meet load reasone, or for redundancy? Or is one dedicated to a particular zone? There may be a method to the madness on the wet side that should be considered on the electrical side.

Also, be aware that some boilers prefer continuous live with a separate enable signal, to allow them run on after **** down to dissipate heat, or they periodically run the pump to ensure it doesn’t seize.

Both boilers run parallel to manage load (it's a big old house) and output back to the same circuit and the valves and pumps on each control the flow of hot water to the zone. The way it's configured now though, you can only have both zones on as the valves are connected to same live/neutral. Each boiler though can run independently and heat both zones, though insufficiently.

The boilers have wires for constant live and switch live feed currently, but both seem to be constant, hence the timer switch does nothing.

I probably need to look at the actuators, I was going to use secure zwave ones, but I guess each will be controlling 2 boilers, their 2 internal pumps, and the zone pump and valve. Need to make sure that load is not too much as well as whether 3a switch would be enough overall.

diggerdigger

Bruthal wrote: »

You could put a 3A fused spur for each boiler.

each of the boilers is on a 3a fuse switch, so good for maintenance, but through a single fuse back up the line.

I didn't check how constant and switched live was handle in the boiler fuse switch.

diggerdigger

So I have looked at the power consumption of the components:
Boiler 1 & Pump 125w
Boiler 2 & Pump 125w
Zone 1 Pump 84w at max pump setting
Zone 1 Motorised Valve 6w
Zone 2 Pump 84w at max pump setting
Zone 2 Motorised Valve 6w

Gives a total of 430w, so I think 3A should be OK overall unless Im missing something?

Actuators are 3A also, and their max should be 340w.

Dardania

Sounds good so, presuming actuators are fed differently?

Whats your plan thereafter - do you want to work in the timer? It might be easier to have a programmable thermostat in each zone, activating its respective zone valve, which then in turn activates the common enable signal to both boilers.

And are you going to do lead / lag? E.g. set the return temperatures of each boiler slightly differently, so as to favor one boiler over another? Might end up being more efficient to fully load one boiler rather than half load 2 if you can.

diggerdigger

Dardania wrote: »

Sounds good so, presuming actuators are fed differently?

Whats your plan thereafter - do you want to work in the timer? It might be easier to have a programmable thermostat in each zone, activating its respective zone valve, which then in turn activates the common enable signal to both boilers.

And are you going to do lead / lag? E.g. set the return temperatures of each boiler slightly differently, so as to favor one boiler over another? Might end up being more efficient to fully load one boiler rather than half load 2 if you can.

I was going to leave in a simple timer in parallel just in case. The actuators are wireless receivers (z-wave) so very low load so fed with constant live from the wiring centre. They will be controlled by wireless thermostats upstairs (this is in basement).

The hot water tank is right at the top of the house, and I can't see any thermostat or link back. Must just be on the top zone heating loop. Will be a pain to put the heating on to heat a tank of water. Maybe I'll check that again when I'm in the mood to wriggle through small cobwebby spaces.

Good point on the lead/lag. Is there a general best practice? I have them both turned down to a lower temp now at the moment as were not yet in the house and with the wiring it's constant off or constant on and I don't want to have it fully off.

Many thanks,

Dardania

Okay I see what you mean with timer - it’ll need to somehow open the actuators to actually dissipate the water somewhere? I’ve seen similar principle done before, but with frost thermostat - but either way it’s a manual override for you in case the fancy controls give up the ghost.

You could consider a tapstat for the hot water cylinder as a simple “prevent over temperature” control, to try not let the water get too far past 60C. Or down the road, go crazy with an evohome type system to do individual control within the zone.

With the lead / lag, and given it’s an old house, chances are the rads were sized on the basis of 80C flow / 70C return temp or thereabouts. I would tend to try 68C for one boiler, 72C for the other, to give enough buffer space between them.
That is, if the boilers can reach such high temps - modern boilers tend to try condense more, so want to run longer at lower temps. But either way, about 4C difference should be adequate to separate them, even if you have to go at lower temps. And to even up run time between each boiler you could switch the lead boiler (lower return temp) every few weeks.

diggerdigger

Dardania wrote: »

Okay I see what you mean with timer - it’ll need to somehow open the actuators to actually dissipate the water somewhere? I’ve seen similar principle done before, but with frost thermostat - but either way it’s a manual override for you in case the fancy controls give up the ghost.

You could consider a tapstat for the hot water cylinder as a simple “prevent over temperature” control, to try not let the water get too far past 60C. Or down the road, go crazy with an evohome type system to do individual control within the zone.

With the lead / lag, and given it’s an old house, chances are the rads were sized on the basis of 80C flow / 70C return temp or thereabouts. I would tend to try 68C for one boiler, 72C for the other, to give enough buffer space between them.
That is, if the boilers can reach such high temps - modern boilers tend to try condense more, so want to run longer at lower temps. But either way, about 4C difference should be adequate to separate them, even if you have to go at lower temps. And to even up run time between each boiler you could switch the lead boiler (lower return temp) every few weeks.

I must try experiment with the temps.

The actuators I meant were just electrical actuators, switching live to boilers and zone motorised valves and zone pump when the thermostat call for heat remotely.

I thought about the evohome but that top zone alone has 16 rads with trvs. So I had to soften my cough on that one.

Now that you mention tapstat, I seem to remember a trv type valve on the tank, so perhaps theres one already there. I must check again.

Dardania

So actuators are remote relays - got you - same principle though they should wire into the motorised valve actuators, which in turn will call in the boilers.

Evohome is expensive, particularly in a 16 rad zone (must be bleedin' massive house!) - but maybe a half way house would be to fit normal TRVs just to prevent room overheating, and you could upgrade the TRV heads over time if you wanted to go for full evohome. Even having simple "overheat" protection will make a big impact on system load, particularly in spring time or autumn.

The website I bought all mine fromw as this: https://www.heatingcontrolsonline.co.uk/radiator-valves-c-28.html/thermostatic-radiator-valves-c-28_37.html?sort=p.price&order=ASC although nowadays amazon has a good range too.

Best of luck!