Willis heater to run UFH

[funks81]

I am considering adding a Willis heater to my UFH in order to take advantage of the cheap overnight Go Faster rates.

 

I have come up with two possible options:

 

I have an unused port on the manifold and was wondering if there was anything stopping me plumbing the Willis heater directly into this.  (It feels wrong - but can't quite work out why!!)

 

Second option is to put the Willis heater onto the heating return.  The possible problem with this is that my flow and return are 22mm and I believe the Willis heaters all have 15mm fitments.  Would it be okay to run the Willis heater in parallel with the existing 22mm return?  (I haven't got room in my CU for 2 x new circuits - as I see people have previously used 2 x Willis heaters in parallel).

 

I don't think the output from the Willis heater is going to be great enough to replace the oil boiler - and I only intend to use it overnight during the cheap rate and revert to heating using the oil boiler during peak periods.  The oil boiler would be switched off during these times.  The heating is an open vented system.  Happy to do the plumbing myself - but would get an electrician to connect to the CU.

 

 

[joth]

1 hour ago, funks81 said:

I have an unused port on the manifold and was wondering if there was anything stopping me plumbing the Willis heater directly into this.  (It feels wrong - but can't quite work out why!!)

 

It's the wrong side of the themostatic mixing valve, so there's a risk it would damage floor finishes via overheating.

[I had similar ideas about breaking the mold by putting a buffer tank on a spare manifold port]

 

1 hour ago, funks81 said:

Second option is to put the Willis heater onto the heating return.

 

Check your boiler doesn't do something weird if the return flow into it is hotter than the set-point temperature. Seems unlikely but who knows.

Otherwise, you could put the Willis heater on the flow rather than the return? Feels safer to me (i.e. Willis can "top up" the boiler temperature, much like they are sometimes used to boost up an ASHP output in very cold climates)

 

1 hour ago, funks81 said:

(I haven't got room in my CU for 2 x new circuits - as I see people have previously used 2 x Willis heaters in parallel).

 

Check if you can put 2x Willis on a single 32A MCB? A pair of fused spur switches (one per Willis) fed by 4mm2 T&E from a single MCB seems legit, but IANAE..

 

 

[funks81]

Regarding the first point about running it on the manifold side of the TMV - I presume in normal operation the Willis heater should cut out once it reaches it set temperature - say 35C.   Obviously the floor overheating only becomes an issue should the inbuilt thermostat fail.  I'm wondering if I got the electrician to fit a pipe thermostat as a backup in the event of the inbuilt thermostat failure - would there be any other reasons not to install this side of the TMV??

 

Obviously makes the plumbing much simpler if it could be installed here!!!

[JohnMo]

Strangely you say a free port, but all ports have pipes connected.  The one without an actuator/ manual valve has pipes connected?

 

The two in parallel could just be 2x units, one duty the other standby. 

 

 

[joth]

35 minutes ago, funks81 said:

Regarding the first point about running it on the manifold side of the TMV - I presume in normal operation the Willis heater should cut out once it reaches it set temperature - say 35C.

This thread touched on running Willis heater without TMV protection and apparently yes they can be turned right down to 30°C so as long as you trust it, seems that would be fine.

Then nice thing with this setup is it only needs the secondary UFH circ pump to run, the primary pump through the boiler can be shutoff completely.

 

You could put a normally-closed manifold valve on that special zone, wired in parallel to the Willis? This will shut off that loop when in normal (boiler) operation which might help avoid it messing with the UFH balancing in normal use. Otherwise a bunch of boiler output will shortcut via the Willis loop and may introduce boiler short-cycling.

 

 

[funks81]

On 22/09/2022 at 15:59, JohnMo said:

Strangely you say a free port, but all ports have pipes connected.  The one without an actuator/ manual valve has pipes connected?

 

The two in parallel could just be 2x units, one duty the other standby. 

 

 

Hi John,

 

I didn't get notified about your response - hence the late reply!!

 

Yes - there are pipes connected - but they've been terminated after about 50cm.  Not entirely sure why it was done this way!!!

 

 

[Nickfromwales]

1 hour ago, funks81 said:

Hi John,

 

I didn't get notified about your response - hence the late reply!!

 

Yes - there are pipes connected - but they've been terminated after about 50cm.  Not entirely sure why it was done this way!!!

 

 

It was to cap off the feeds properly, as most installers aren’t happy just putting a cap / blank on the underside of the manifold ergo a bit of pipe and then a 16mm cap end gets fitted. Odd that they did not just supply / fit the correct manifold for the application? What gives?

 

First thing to consider here, is; what is the kW of heat input required at the time you wish to invest the heat from electricity? If you go all the way and add 2 x 3kW Willis then you’ll get far more meaningful  reinforcement. You don’t seem to state if you wish to fortify with the Willis / GO! or stop the oil from burning altogether? 

 

On 22/09/2022 at 13:27, funks81 said:

(I haven't got room in my CU for 2 x new circuits - as I see people have previously used 2 x Willis heaters in parallel).

You can take a bigger supply cable from a single 40a circuit, and then take that to a second ‘mini CU’ supplying 2x 16a MCB’s to 2x Willis. Or you can cut into the meter tails and add the second CU there. Plenty of options tbh to get 2x Willis in, or even 3x  

 

IMHO if you’re going to do this, it should be with a view to stopping oil being consumed. You’re just not going to replace 12kW of input with GO! Unless you add more Willis units. Certainly something i would not write off as a possibility if the long-term economics say this is a robust pursuit  

Edited September 27, 2022 by Nickfromwales

[PeterW]

Something weird about that manifold and how it’s piped as there is a thermostatic valve but the pump is on the wrong end ..? Unless the lockshield on the top rail is closed it looks like the pump just circulates across the manifold rails…? 
 

Any pipework begin the pump ..?

[funks81]

On 27/09/2022 at 23:26, PeterW said:

Something weird about that manifold and how it’s piped as there is a thermostatic valve but the pump is on the wrong end ..? Unless the lockshield on the top rail is closed it looks like the pump just circulates across the manifold rails…? 
 

Any pipework begin the pump ..?

It is certainly rather different to others - but its the way that Uponor like to have it set up.

 

Flow comes in at the thermostatic valve - which has a remote sensor pocket - just above the pump.  The lock shield on the top rail (just before the return) is partially closed forcing most of the flow around the UFH circuits.