Immersion smart switch

[vk2003]

We recently had our vaillant (3 year old) boiler fail with an F75 pump error.

Whilst the boiler is under warranty, it has taken several days for them to come out to repair.

Fortunately our large hot water tank has 2 x 3Kw immersion heaters for emergency use. The tank and pair of power switches are in the plant room in the loft. Whilst it isn't the end of the world to trek to the loft to switch them on and off to heat water, we did manage to leave them on a couple of times all day.

 

Can anyone recommend a smart switch which can be used to switch these on and off manually and on a timer if required?

Our heating thermostats in each room are made by nuHeat - I know they do smart switches, but are they any good and can they cope with a 6Kw load?

[MJNewton]

Given that the dependency on the immersion heaters is a rare occurance, is it not sufficient to leave the switches on all day when required with the thermostats preventing power being continuously drawn? If you're not using hot water heat loss will be minimum, and if you are then the stats will just top things up as required. I can't imagine there's much energy to be saved by having greater manual control in such rare circumstances. 

[vk2003]

Thanks for your reply. The problem in our house is that the hot water circuit is very large. Consequently, a pressurised system wasn't suitable. In order to ensure hot water reached the taps quickly, a secondary water circulation system was specified by the plumber.

The hot water is constantly circulated around the house; as a result the water in the tank constantly loses heat during this circulation. Ordinarily, the boiler is left to constant (poor energy efficiency I'm afraid) for hot water.

However, when using the immersion, this gets expensive! Hence the desire to make it easier to use, and avoid running the immersions all day. It only takes ~45 mins for a full tank of water.

[MJNewton]

Ah, okay, I can understand the need more now. 

 

I think I am still thinking that by the time you've found and fitted a solution the problem will have gone away, and hopefully never to return! 

[ProDave]

I would look at putting the HW circulation system on timers, or room occupancy sensors, so it only circulates when the rooms with taps are in use.

[PeterW]

1 hour ago, ProDave said:

I would look at putting the HW circulation system on timers, or room occupancy sensors, so it only circulates when the rooms with taps are in use.

 

This is quick and cheap and a must have irrespective of the timer issue.

 

For a smart switch, a 16A Sonoff will do it no problem. One per immersion, controlled over wifi.

 

For the circulation pump, just use a simple 24hr mechanical rotary time switch, give it 15min/hour over 6am-11pm and it will save you a large quantity of money and prolong the life of the pump - the one I fitted saved £175 in its first year off heating water.

[Jeremy Harris]

4 hours ago, vk2003 said:

We recently had our vaillant (3 year old) boiler fail with an F75 pump error.

Whilst the boiler is under warranty, it has taken several days for them to come out to repair.

 

 

Not related to your question, but the F.75 error is fairly common and can be prevented, but Vaillant are a PITA over the cause of this.  We battled with repeated F.75 errors on the boiler at our old house, and eventually found a 100% solution for them (after more than 20 call outs under warranty).  The fault has two known causes, both stemming from the same pressure sensor inside the boiler.  The sensor tries to detect the pump pressure "kick" as it starts, but this "kick" is tiny, especially on a big system that has a fairly low flow resistance. 

 

The most common cause for this fault is the pressure sensor being blocked by debris.  This was the "go to" approach taken by everyone that came to see our boiler - debris must be blocking the sensor, so they replaced the sensor each time, only for the fault to recur a week or two later.  For us, it turned out that debris wasn't the problem, as we'd fitted a Magnaclean filter on the return right next to the boiler, and examination of the tiny hole in the sensors that had been removed showed they were clean as a whistle, but it's very easy to see how just a small amount of debris could block this sensor port.  So, making sure there is a good filter on the boiler return, and making sure that it's regularly cleaned, is important to reduce the risk that the sensor will get clogged.

 

The other cause is if the system is large and has a very low flow resistance.  The problem is that the margin between the static pressure in the system and the tiny pressure "kick" from the pump can be low, especially when all the TRVs are wide open, so making operation a bit unreliable.  The boiler will try to fire three times before throwing an F.75 fault and locking out, so this problem can go undetected for a time, as the chances are that one start out of the three will be OK, so no fault will be flagged.  The fix for this is a modification kit available from Vaillant to reposition the pressure sensor to a location higher up inside the boiler.  Once fitted, this modification kit completely removes the F.75 fault problem.  The kit is called an "F.75 modification kit" by Vaillant, believe it or not, although it seems that Vaillant installers may not be aware of it (those that installed our boiler knew nothing about it - I only found out about it from making enquiries on the web).

[gravelld]

Why don't you just use mechanical timers for the immersion heaters?

[Vijay]

Love posts like this that show what's possible.

 

Out of interest, has anyone come across boiler timers that can be fitted that you can control by an app?

Edited May 10, 2019 by Vijay

[dpmiller]

cheapo chinesium wifi thermostat.

[SteamyTea]

If it is on its own circuit, which I think it should be, just flick them on and off at your consumer unit.  Saves getting the step ladder out.

[vk2003]

On 10/05/2019 at 15:43, JSHarris said:

Thanks for this.. Will get my plumber to do this at next visit.

 

On 10/05/2019 at 15:43, JSHarris said:

Not related to your question, but the F.75 error is fairly common and can be prevented, but Vaillant are a PITA over the cause of this. 

...........

The fix for this is a modification kit available from Vaillant to reposition the pressure sensor to a location higher up inside the boiler.  Once fitted, this modification kit completely removes the F.75 fault problem.  The kit is called an "F.75 modification kit" by Vaillant, believe it or not, although it seems that Vaillant installers may not be aware of it (those that installed our boiler knew nothing about it - I only found out about it from making enquiries on the web).

 

[vk2003]

Further to the modification kit for the sensor, I understand the part number from Vaillant is 0020023721

[vk2003]

On 10/05/2019 at 15:11, PeterW said:

For the circulation pump, just use a simple 24hr mechanical rotary time switch, give it 15min/hour over 6am-11pm and it will save you a large quantity of money and prolong the life of the pump - the one I fitted saved £175 in its first year off heating water.

 

Quick question: did you find that running the circulation pump for 15 mins/hr gave a longer lead time at the taps for hot water?

Following on from your comment I thought about switching off the circulation and the hot water when we aren't in the house...

[PeterW]

On 19/05/2019 at 10:23, vk2003 said:

 

Quick question: did you find that running the circulation pump for 15 mins/hr gave a longer lead time at the taps for hot water?

Following on from your comment I thought about switching off the circulation and the hot water when we aren't in the house...

 

15m/Hr is a lot more than you actually need, as you can do some very quick and dirty calculations on flow rate of circulation pumps and also the thermal losses from the pipes. 

 

If you have a 50m loop of 22mm pipe, then thats 15 litres of water. Assuming bare minimum insulation and a starting temperature of 47c, this will cool to around 39c over 45 mins in ambient (19c) air space. That loss is negligible and tbh is offset by the massive saving in running the pump for the remaining time anyway. You can get away with 2min/hour for that sort of pipe volume however it does mean finding a custom timer and these are normally DIN rail, need enclosures and are £75-100 by the time you've installed vs a £15 timeclock that can be replaced easily from any DIY shed.

 

I'd caution against any "off switch" for the house, as you'll forget and end up not turning it back on...

[Ed Davies]

2 hours ago, PeterW said:

You can get away with 2min/hour for that sort of pipe volume however it does mean finding a custom timer and these are normally DIN rail, need enclosures and are £75-100 by the time you've installed vs a £15 timeclock that can be replaced easily from any DIY shed.

 

How about a thermostatic switch on the pipe by the slowest-to-reach tap?

[vk2003]

PeterW

Thanks for the further detail. I'm convinced!