Help with a relay box rewire

[HRP123]

Hi there thanks for your time to look at this.

I've got a multi pump / circuit system which is connected via a relay box to the boiler and Honeywell timer programmers. Picture attached.

Right now any single circuit can turn the boiler on an off at any time (assuming the programmers allow it). There are central heating (two zones), towel rails (one zone), underfloor heating (two manifolds) and hot water cylinders (2 of them).

I'm trying to rewire the system to make it hot water priority. So basically if the hot water circuit calls for heat, then the other circuits should go off temporarily to allow it to reach temperature as quickly as possible. This should allow me to range rate the boiler down (40kw current) and ensure it doesn't burn crazy amounts of gas trying to satisfy all open circuits at once.

I cannot see any diagrams online for these kinds of relays - I cannot even see the name of the product (generic plastic box). Can anyone help?

Thanks!!

 

[Timmy D]

John will probably be along with the data but I see no real reason for doing this.

Can’t see any big savings to be made. The hot water cylinders need x amount of energy to heat, the house has heat losses and needs y amount of energy to heat.

Hot water priority/range rating aren’t going to change the energy needed.

 

[Chuck]

Looks home made by a DIYer to me. (No strain relief, seems to be using the green/yellow core in mains cable for something other than grounding, etc.) It's what we call a 'death box'.

 

[ShaunCorbs]

Find the hot water relay there should be a normally closed terminal feed the ch zones from this eg remove the common live and install it into the Nc terminal

This means you would have to leave the hot water on permanently and let the stat do the work once satisfied it would allow you to use your heating

They look like finders should have model number on the side of the relay part

A1 is your live switch
A2 neutral
Note this can be flipped

Com is your perm live should be

No should be your call when the stats are calling for heat

Nc should be empty

 

[HRP123]

John will probably be along with the data but I see no real reason for doing this.

Can’t see any big savings to be made. The hot water cylinders need x amount of energy to heat, the house has heat losses and needs y amount of energy to heat.

Hot water priority/range rating aren’t going to change the energy needed.

Actually as this is a heat only boiler I'm trying to use controls and some manipulation to reduce consumption, as for some reason (not sure if it is the LLH or something about the setup) it does not modulate down well enough.

What I have found is that by range rating it down 40% I can get the flow temperature for the underfloor heating and radiators (assuming they call for heat at the same time) down to a level which they don't need to be mixed (making it more efficient, less cycling etc). However if the HW comes on at the same time, it strains the system as the flow cannot meet the required tank temperature.

 

[ShaunCorbs]

Might be worth changing the boiler so you can have two different flow temperature?

 

[HRP123]

Find the hot water relay there should be a normally closed terminal feed the ch zones from this eg remove the common live and install it into the Nc terminal

This means you would have to leave the hot water on permanently and let the stat do the work once satisfied it would allow you to use your heating

They look like finders should have model number on the side of the relay part

A1 is your live switch
A2 neutral
Note this can be flipped

Com is your perm live should be

No should be your call when the stats are calling for heat

Nc should be empty

Thanks for this. What I am going to try first is to use my controls / programmers to try and work out when HW demand is most likely and see if I can prioritise hot water manually. If I cannot, then I will get someone to help me rewire the box with the kind help of your guidance above. Thanks!

 

[HRP123]

Might be worth changing the boiler so you can have two different flow temperature?

Yes this is what I first thought about doing, although this will cost around £4,000-5,000 - so I'm not whether it is worth spending that when the current boiler still works. Ideally I was thinking if I can wait it out 2-3 years then heat pumps / costs may come to a point where they are a better option than currently.

 

[HRP123]

Looks home made by a DIYer to me. (No strain relief, seems to be using the green/yellow core in mains cable for something other than grounding, etc.) It's what we call a 'death box'.

Hence I don't want to call the original plumber back for this!

 

[ShaunCorbs]

Yes this is what I first thought about doing, although this will cost around £4,000-5,000 - so I'm not whether it is worth spending that when the current boiler still works. Ideally I was thinking if I can wait it out 2-3 years then heat pumps / costs may come to a point where they are a better option than currently.

And then inflation rises again so everything is 15% more expensive etc

 

[HRP123]

John will probably be along with the data but I see no real reason for doing this.

Can’t see any big savings to be made. The hot water cylinders need x amount of energy to heat, the house has heat losses and needs y amount of energy to heat.

Hot water priority/range rating aren’t going to change the energy needed.

That is what I originally thought but the problem is when set to a higher total output the boiler does not modulate down well enough when only a few circuits are open.

 

[HRP123]

And then inflation rises again so everything is 15% more expensive etc

Yep, for boilers ... although I wonder if graduallly declining demand for gas boilers will constrain price rises. I think the price of heat pumps will come down with greater production / installation capacity and perhaps even govt support.

 

[ShaunCorbs]

I don’t think it will for at least 10 years

 

[gmartine]

You can't have both if that's what you're implying, once the heat pump market is more established and competition affects pricing government support will be withdrawn as that is the nature of support as the market takes hold.

In your case I think it's a false economy waiting to upgrade considering the many thousands you've been paying to heat your place with a malfunctioning system/design and elderly boiler. All the tinkering in the world won't get the system performance to where you want it to be and I'd expect any upgrade outlay made soon you'd get back in reasonable time considering the size and demands of your system.

 

[HRP123]

Thanks for your thoughts. I'm trying exactly how the savings will come from spending on a potential boiler upgrade -

Presumably the gains from a new boiler are
1. Slightly higher efficiency ratio
2. Lower minimum kw burn rate (between 2-3kw vs current 9kw)
3. Weather compensation (but is this possible with modern heat only boilers? - see below)

Are these modern heat only boilers able to have different flow temperatures for hot water vs heating circuits? If these new boilers still need mixing valves for the heating circuits?

I've seen that the Viesmann 200w is highly recommended however this comes with a more expensive capital outlay and it appears fewer engineers who work with them. The WB Life would be easier to fit and cheaper but has a higher min kw (around 3kw I think).

I'm already in the process of installing all Nest thermostats so I can control and manually adjust things as easily as possible. Have been running the boiler successfully range rated down to around 24kw instead of 40kw. I've just installed an Eddi to make use of solar excess from the recently installed solar panels.

The main issue I find is that the minute the underfloor heating (only) calls for heat, this seems to burn a much higher amount of gas (based on 30 min meter reads) than what the theoretical value should be. So lets say the u/f heating area open is 100m2 x 100w = this should be 10kw right? The boiler almost always will burn close to the max (e.g. 20-24kw) when trying to satisfy just this need.

 

[ShaunCorbs]

As your on ufh you want the lowest possible kw

4 pipe with the viessmann 200 system allows your cylinder to heat to 65 and one circuit to be what ever you want temp wise

The Worcester you need a system boiler with the optional diverter kit

A heat loss is the only way but I would be surprised if you needed over 20kw

 

[HRP123]

As your on ufh you want the lowest possible kw

4 pipe with the viessmann 200 system allows your cylinder to heat to 65 and one circuit to be what ever you want temp wise

The Worcester you need a system boiler with the optional diverter kit

A heat loss is the only way but I would be surprised if you needed over 20kw

Do you have a strong view yourself on whether the Viessman is worth the extra £500-1,000 installed over the WB?

 

[ShaunCorbs]

For the modulation I would go with the better one eg lower kw but Heatloss the property first

 

[HRP123]

For the modulation I would go with the better one eg lower kw but Heatloss the property first

I have actually done the Heatloss - it showed 20kw.

 

[ShaunCorbs]

Do you have cavity wall insulation?

 

[HRP123]

Do you have cavity wall insulation?

Yes the house is insulated - new build in 2008

 

[John.g]

Thanks for your thoughts. I'm trying exactly how the savings will come from spending on a potential boiler upgrade -

Presumably the gains from a new boiler are
1. Slightly higher efficiency ratio
2. Lower minimum kw burn rate (between 2-3kw vs current 9kw)
3. Weather compensation (but is this possible with modern heat only boilers? - see below)

Are these modern heat only boilers able to have different flow temperatures for hot water vs heating circuits? If these new boilers still need mixing valves for the heating circuits?

I've seen that the Viesmann 200w is highly recommended however this comes with a more expensive capital outlay and it appears fewer engineers who work with them. The WB Life would be easier to fit and cheaper but has a higher min kw (around 3kw I think).

I'm already in the process of installing all Nest thermostats so I can control and manually adjust things as easily as possible. Have been running the boiler successfully range rated down to around 24kw instead of 40kw. I've just installed an Eddi to make use of solar excess from the recently installed solar panels.

The main issue I find is that the minute the underfloor heating (only) calls for heat, this seems to burn a much higher amount of gas (based on 30 min meter reads) than what the theoretical value should be. So lets say the u/f heating area open is 100m2 x 100w = this should be 10kw right? The boiler almost always will burn close to the max (e.g. 20-24kw) when trying to satisfy just this need.

Just came across this thread, the UFH may be using 20 to 24kw if you are happy with the 30 minute readings, don't know how these are taken but I would certainly verify them by taking say exactly a 60 sec reading between photos of the REAL Gas Meter in M3, that will prove the readings one way or the other.

I think I asked in your other post how many loops etc is emitting this 20 to 24kw as a loop should, with a flowrate of 2LPM and a 7C to 8C dT, emit ~ 1kw, you should be able to read off the flowmeters flow rate in LPM and knowing the manifold flow/return temps calculate reasonably accurately the heat demand.

 

[HRP123]

Just came across this thread, the UFH may be using 20 to 24kw if you are happy with the 30 minute readings, don't know how these are taken but I would certainly verify them by taking say exactly a 60 sec reading between photos of the REAL Gas Meter in M3, that will prove the readings one way or the other.

I think I asked in your other post how many loops etc is emitting this 20 to 24kw as a loop should, with a flowrate of 2LPM and a 7C to 8C dT, emit ~ 1kw, you should be able to read off the flowmeters flow rate in LPM and knowing the manifold flow/return temps calculate reasonably accurately the heat demand.

Thanks for this follow up post, appreciated. So I had a look at the manifolds - they each have 8 loops. One of the manifolds does not have flow meters. Going to try and observe the flow rate on the other manifold one of these days.

I have checked the home hub readings against the gas meter and it is correct. I have a Ring camera position with snapshot history so in real time I can see which heating circuits/pumps are open, and the past half hour gas consumption readings.

For example last night I left only the underfloor heating on overnight to do a test. It showed that each hour it was on, the gas consumption was around 22kwh per hour (around the range rated max output). UF loops wise I cannot tell exactly was on but I think it may have been around 100m2 which is you assume is 120 watts psm = 13kwh theoretical usage? Let's say even 15kwh with inefficiencies. So wondering why this is coming out to close to the max output the boiler is range rated too instead of 15kwh.

Really appreciate the time you are taking to provide help.

 

[HRP123]

Just came across this thread, the UFH may be using 20 to 24kw if you are happy with the 30 minute readings, don't know how these are taken but I would certainly verify them by taking say exactly a 60 sec reading between photos of the REAL Gas Meter in M3, that will prove the readings one way or the other.

I think I asked in your other post how many loops etc is emitting this 20 to 24kw as a loop should, with a flowrate of 2LPM and a 7C to 8C dT, emit ~ 1kw, you should be able to read off the flowmeters flow rate in LPM and knowing the manifold flow/return temps calculate reasonably accurately the heat demand.

Sorry just read again you were mentioning based on loops - let's say half the 16 total loops or 8 loops were on - this should work to 8kwh.