Combi with a 300 litre hot water tank

[Chris Hex]

I have been asked to provide a wiring centre for a combi boiler providing hot water to two showers a 300 litre hot water tank and central heating. The heating engineer says he is going to provide two two valves. I'm just a little confused as to how the thermostat on the tank will call for the water to be heated. I thought with a combi it relied on water being used, it then provided instant hot water. So I can't see how if the tank cools down how it is going to call for heat, unless its plumbed into the central heating.

Has anyone dealt with this before?

 

[Leesparkykent]

You sure it's a combi and not a system boiler?

Edit: the showers come of the boiler and not the cylinder?

 

[snowhead]

Forget it's a Combi, that side has no external controls.

Just treat it as a heat only boiler with one zone for heating and the other for hot water.

 

[buzzlightyear]

I have been asked to provide a wiring centre for a combi boiler providing hot water to two showers a 300 litre hot water tank and central heating. The heating engineer says he is going to provide two two valves. I'm just a little confused as to how the thermostat on the tank will call for the water to be heated. I thought with a combi it relied on water being used, it then provided instant hot water. So I can't see how if the tank cools down how it is going to call for heat, unless its plumbed into the central heating.

more like a open vented boiler .

 

[Leesparkykent]

more like a open vented boiler .

More like an unvented system.

 

[buzzlightyear]

Open Vent Boiler – Vokera - http://www.vokera.co.uk/homeowners/boilers/open-vent-boilers/

 

[Leesparkykent]

Open Vent Boiler – Vokera - http://www.vokera.co.uk/homeowners/boilers/open-vent-boilers/

Yeah I know what open vented is and combi isn't as it's pressurised so the system will be unvented.

 

[Chris Hex]

You sure it's a combi and not a system boiler?

Edit: the showers come of the boiler and not the cylinder?

Definitely a combi, showers defiantly coming off the combi and not the tank.

 

[Simon79]

As Snowhead says just wire as standard s-plan

 

[Corbs]

S plan the heating

Unvented cylinder will be heated by the heating coil

As the lads have said ignore the hot water side of the combi



Normally fit an unvented cylinder with a combi if they have a big bath or a few baths etc (high draw items)

 

[Chris Hex]

Forget it's a Combi, that side has no external controls.

Just treat it as a heat only boiler with one zone for heating and the other for hot water.

Thanks , that is the only way I could see it working, the tank is a second heating zone.

 

[Leesparkykent]

Definitely a combi, showers defiantly coming off the combi and not the tank.

Yeah as already mentioned..it's an S-plan.

 

[Chris Hex]

S plan the heating

Unvented cylinder will be heated by the heating coil

As the lads have said ignore the hot water side of the combi

View attachment 38406

Normally fit an unvented cylinder with a combi if they have a big bath or a few baths etc (high draw items)

Thanks

 

[LankyWill]

Bigger question why didn't they spec a system boiler and an unvented cylinder?

 

[Chris Hex]

Bigger question why didn't they spec a system boiler and an unvented cylinder?

I think the landlord has got bad advice. It's a 6 bed HMO, if it was all ensuite he would need the 300 litre tank to run the other showers. As it is I think the tank is providing water to basins, sinks and appliances. Overkill if you ask me. System boiler wasn't specified as the combi was already installed. The heating engineer did question the decision but the landlord was insistent. Ho hum.

 

[PEG]

Hi,just out of curiosity,how many Kw is the combi boiler?

 

[Chris Hex]

Hi,just out of curiosity,how many Kw is the combi boiler?

I didn't look, left it to the Gas safe guy.

 

[snowhead]

I think the landlord has got bad advice. It's a 6 bed HMO,

If the Landlord has other HMOs then they probably have the best idea of what suits that type of property.

 

[Chris Hex]

If the Landlord has other HMOs then they probably have the best idea of what suits that type of property.

It's his first so I think he has got confused advice. I have a couple of HMO's with a business partner. We use a 300 litre tank when we have 5 ensuites with showers. 2 run off electric leaving the 300 litres tank to deal with the remaining 3 showers. We use a system boiler instead of a combi.

 

[Wilko]

Using a combi to run multiple showers is not going to work for the tenants, I would have thought.

 

[MJPD29]

Sure the combi heats the water as required and the stat doesn't need to call for it? Unless I am missing something

 

[Wilko]

It will depend on the HW flow rate of the combi they've picked. A good one will run a shower fine, but maybe not 2 or 3. Could try restrictors on the showers to get over this I guess (?).

 

[Leesparkykent]

combi boilers, imo are useless with more than 1 shower.

 

[David M]

It will depend on the HW flow rate of the combi they've picked. A good one will run a shower fine, but maybe not 2 or 3. Could try restrictors on the showers to get over this I guess (?).

Won't make much difference, you just can't get the volume of water required because of the way instant hot water systems work.

 

[David M]

Using a combi to run multiple showers is not going to work for the tenants, I would have thought.

Correct, you wouldn't spec a combi boiler for multiple showers that are likely to be used simultaneously. A pressurized system boiler with suitably sized hot water storage tank is going to be more cost effective and better for the job.