Back boiler and electric boiler on the same system?

[Bob Hill]

Hi all,

So i've had a request from someone to look into the possibility of fitting an electric heater onto their existing back boiler system.

Their set up is:

Coal fired back boiler which serves a cylinder (with immersion heater for back up) and about 6 standard sized rads (mix of single and double panel). The Hot water is gravity and the heating has an ancient circulation pump on it. The system is open vented (though the vent for the heating side is only in 15mm which seems worrying to me - still it's been working fine up till now).

They were looking at a heatre sadia Amptec: Heatrae Sadia
It's basically a big heat exchange tube as far as I can fathom.

I've heard that these may end up being more costly to run that the larger electromax ones which include a cylinder and can heat water at off peak and store it for later.

They don't want the hassle of decommissioning the back boiler so were thinking of leaving it as part of the system (A big dead leg I guess...)


My thinking is the following:

The system could be upgraded to a 3 way mid position valve (with suitable controls) to allow separate hot water and heating and the electric boiler could be fitted. The problem with this is that should the back boiler ever be used this could create a situation where hot water is pushing against a closed 3 port valve.

The second issue is that the electric boilers have a thermal cut out of about 95-100 degrees which could be tripped should the back boiler be used.

I'd be interested to hear what others experiences and recommendations are in this situation - feel free to tell me i'm being stupid and have forgotten something obvious (but be nice) 🙂

Thanks in advance.

 

[erj]

back heel it, it is going to cause a lot of problems.
If they dont want the back boiler disconted it is going to cause a lot of problems, walk away

 

[lame plumber]

put in anything except an electric boiler, they must be mad or landlords who dont have to pay the running costs

 

[Bob Hill]

Hi guys, might you be able to expand on the kind of problems they'll get? And could you point me to more info on the electrical costs of electric boilers?

I'm keen to give good advice and reasons why they shouldn't go ahead with their plans.

 

[01ST13795]

The cost of running an electric boiler is ridiculous!!!

 

[lame plumber]

needs a rather large lump of twin and earth to come off consumer unit, which indicates the running costs as well

 

[josh]

I don't see why you would want to do that anyway.

 

[Bob Hill]

The logic is that they are fed up with lighting fires and carrying coal etc. they are spending a lot on coal each month. they don't have gas to the property so no combi boiler. thus they are thinking an electric boiler may be a relatively cost effective option by comparison. what might you suggests as an alternative?

 

[josh]

I see, i wasn't snubbing the electric boiler just the marrying the two things up.
You'v got renewables but their expensive to buy/install and not normally suitable for retro fits without bringing the propery upto high insulation standards which are not allways possible so would rule that out.

Oil which is certainly possible as the solid fuel boiler could be done away with and the system configured for an oil boiler or LPG. Could even be linked together using a buffer/accumulator but again how long is a piece of string?

 

[Bob Hill]

Thanks. I did have a rather crazy thought that you could use a bottled gas powered fire instead of the coal one. Seems best to advise them that if it isn't broke then don't fix it.

 

[josh]

you'd forever be running out of gas if it were to be for the whole house plus compared to a proper LPG tank bottles are expensive.

 

[Bob Hill]

So to try and summaries and check i've got it right:

1. An electric boiler is likely to be expensive to run. It is not likely to work well if the back boiler is left in the system - there will be lots of problems even if you put proper controls on (could someone explain why this would be to help me understand?).

2. LPG or Oil replacement boilers are possible (But I guess again would need the back boiler removed?)

2. Solar or something similar is an alternative.

I guess the conclusion I think we've come to is that there isn't really a short cut way of upgrading the system, it's either stick with what you've got or invest a lot in completely changing everything.