No boiler bypass needed?

[garmcqui]

Evening all,

I'm Installing a basic thermostat system onto my parents 25 year old oil-fired central heating system (no gas as it's N. Ireland). The images below show the oil boiler setup located in the garage:

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• garmcqui
• 24 Mar 2015
• 1

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• garmcqui
• 24 Mar 2015
• 1

At the moment, there is no control. At all. Just on-off. As a result, they are heating a large house (25+ radiators) pretty much all the time, which is costing £3k+/yr in oil

I'm planning on installing a couple of Honeywell zone valves (for CH & DHW), controlled by a programmable thermostat. I'll use the zone valve end switches to switch on the boiler & pump. Effectively it'll be an S-Plan system.

Now I'm no plumber, but my dad and I will manage to splice in the two zone valves. What I don't want to do is have to install a boiler bypass etc.

My question is - as there is no pump overrun, can I get away without a bypass? After all, both zone valves will NEVER be closed whilst the boiler/pump are on. They can't be.

If the system is ever updated to include boiler with pump over run, I'll have a bypass put in then.

Cheers

 

[manortim]

If you install zone valves you will need a bypass if you add thermostactic valve.

If you do not install trv's then due to lack of pump over run, you'll not need a bypass.


3k per year on oil for a 25 rad system inhabited by elderly folks who likes their home warm sounds about correct. You could save circa 500 a year with your plans so not a bad investment.

Were you to upgrade to a condensing boiler at a cost of circa 2.5k....expect savings of circa 1000 At best. (including the 500 for the correct controls)

 

[garmcqui]

Thanks for replying.

Sorry, I might be being thick, but explain to me why I need a bypass.

I understand that the zone valves closing will block off the heating and hot water circuits completely, and that you don't want the pump trying to pump against closed valves, but the pump can't physically be running if both valves are closed.

 

[simond]

In the CH circuit, the fitment of TRVs to the rads would require a bypass... however, you are no doubt going to do the job properly and fit a room stat in one of the rooms, and leave out the TRV. In which case, as you say, no bypass is needed.

One thing you need to bear in mind is the change in the hydraulics to the system when the zone valves are inserted. The open vent and cold feed should not be interrupted by zone valves and you should design the new layout to remove the significant risk of 'pumping over' round the F&E tank.

 

[garmcqui]

Yes, I was intending to leave the radiator in the hall without TRV as that is where the programmable thermostat will reside.

As for the hydraulics part of your post, you've lost me! I was intending fitting the zone valves out at the boiler, where the hot water leaves the boiler.

 

[xr4x4]

Do your rads (how many?) have thermostatic valves on them?

 

[garmcqui]

Only a couple currently have TRV's on them. I was planning on fitting TRV's to the rest (apart from the ones in the hall) at the same time as fitting the zone valves (might as well do it whilst system is drained down).

One thing you need to bear in mind is the change in the hydraulics to the system when the zone valves are inserted. The open vent and cold feed should not be interrupted by zone valves and you should design the new layout to remove the significant risk of 'pumping over' round the F&E tank.

The yellow boxes on the diagrams show where I was planning to fit the zone valves:

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• garmcqui
• 24 Mar 2015
• 1

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• garmcqui
• 24 Mar 2015
• 1

I'm unsure where the open vent is joined into the system, it's nowhere near the boiler (as it's in the garage).

 

[xr4x4]

You need the bypass if all the trvs shut down and the pump and boiler doesn't, the heats got to go somewhere.

Would fairly easy to do according to your diagram.

 

[Agile]

Excuse my curiosity but why do they need ALL 25 rads on all the time?

Are ALL the rooms occupied all the time?

Is it a B&B or similar?

Tony

 

[garmcqui]

Excuse my curiosity but why do they need ALL 25 rads on all the time?

Hi Tony, no not all 25 radiators are on all the time. But it's an old house and they don't want damp setting in, so it's on at some point every day in every room. Also I don't want my 70yr old mother having to keep going round bending over to turn radiators on and off several times a day, hence the upgrade to thermostat/TRV's.

 

[JohnD]

you might consider putting the room stat in the living room that is most often used.

It was quite common in the 1960's to put the stat in the hall, but that is the room whose temperature is least interesting. I'm told people used to turn the temp down or up when they went out/came in, but you will have a timer to manage that.

A programmable thermostat like a Honeywell CM907 will enable you to set temps per time per day, so cooler during the night, warmer during the evening, bit lower during the day when people are active etc and it will follow this programme without intervention, though it can be overridden at will.

Some people like wireless stats, but IMO that just gives something extra to go wrong.

 

[Nige F]

It was quite common in the 1960's to put the stat in the hall, but that is the room whose temperature is least interesting. I'm told people used to turn the temp down or up when they went out/came in,

.

Interesting you should mention that it's just what we do with the ancient timer set to constant and growling away in the cupboard. It's got a night set-back to 15degrees provided I don't forget to turn it down

 

[regsmyth]

but the pump can't physically be running if both valves are closed.

Unfortunately it can, as sometimes a valve can close without tripping the microswitch.