Central Heating Modifications – Set up . Commissioning

[GoodDIYjob]

Shouldn't be necessary IMO except that the pump head is vert low when on Auto.
Are all the rads heating up if CH only on? and not heating up if HW heating on as well?.

Try and get a few pump readings when you can (on auto) might be interesting?.

Ok.

Yes, that seems to be the problem. Very little heat from downstairs rads when hot water zone valve is allowing flow to coil.

Will try and get readings and will report back.

Thanks a lot for all these replies and advice.

 

[fixitflav]

Sorry. Not a full explanation. The hot water tank supplies only a second shower upstairs. Oh and the basin that's it.

Downstairs bathroom and kitchen sink off combi.

The new Vaillant has output 26kW (combis sized for instantaneous HW). The previous heat-only boiler likely much lower, so the potential of the Vaillant isn't being used. Just a comment, I realise it doesn't solve anything.

 

[GoodDIYjob]

The new Vaillant has output 26kW (combis sized for instantaneous HW). The previous heat-only boiler likely much lower, so the potential of the Vaillant isn't being used. Just a comment, I realise it doesn't solve anything.

Yes. Thanks. Agree. Had I been asked for my opinion before it was installed, I would of said replace like with like. I.e. a conventional heat only boiler.

It is wrong on so many levels

#Required more pipework adaptions than if heat only boiler replaced.
#Oversized capacity
#Oversized physically (much larger than the old baxi heat only)
#Worse, still, it doesn't fit with the solar energy overflow going to the Hot Water tank, as it removes two sources of use, the downstairs bathroom and the kitchen.
#It is so silly, as the new bathroom downstairs has a bath and a shower and when that is used, there is also a tank full of heated hot water going to waste. Upstairs bathroom is the only thing fed of the hot water tank and it only has a shower and basin.
#The only rationale I could of accepted is perhaps for instantaneous heat at the kitchen sink as the boiler is very close, but still, not worth it for the downsides and compromises. And having plumbed the downstairs bathroom off the combi dhw out just makes a a very silly set up.

Also the controls he has, Nest, doesn't allow any modulation variation for flow temp as it is opentherm. It is aslo compromised by needing to heat the hot water in the tank to a safe level, so I can't see him lowering it below 64C. Maybe a whole new set of Vaillant smart thermostats may help but not sure it would be justified economically even now, especially when the nest was only purchased 18 month ago....

 

[fixitflav]

Yes. Thanks. Agree. Had I been asked for my opinion before it was installed, I would of said replace like with like. I.e. a conventional heat only boiler.

It is wrong on so many levels

#Required more pipework adaptions than if heat only boiler replaced.
#Oversized capacity
#Oversized physically (much larger than the old baxi heat only)
#Worse, still, it doesn't fit with the solar energy overflow going to the Hot Water tank, as it removes two sources of use, the downstairs bathroom and the kitchen.
#It is so silly, as the new bathroom downstairs has a bath and a shower and when that is used, there is also a tank full of heated hot water going to waste. Upstairs bathroom is the only thing fed of the hot water tank and it only has a shower and basin.
#The only rationale I could of accepted is perhaps for instantaneous heat at the kitchen sink as the boiler is very close, but still, not worth it for the downsides and compromises. And having plumbed the downstairs bathroom off the combi dhw out just makes a a very silly set up.

Also the controls he has, Nest, doesn't allow any modulation variation for flow temp as it is opentherm. It is aslo compromised by needing to heat the hot water in the tank to a safe level, so I can't see him lowering it below 64C. Maybe a whole new set of Vaillant smart thermostats may help but not sure it would be justified economically even now, especially when the nest was only purchased 18 month ago....

Yes, it looks like your FIL has been royally ripped off. Simple boiler swap would have done the trick!
From your sketch, the HW function of the combi is not being used (unless it's just not shown, the cold water in isn't shown either). Also if it's like that there will be a problem of unwanted flow through the rads when HW called. The CH return pipes should be commoned before the HW return connection.
If the house heating is poor, sounds like the 64° flow temperature is too low. Unlilkely, but worth checking the boiler output hasn't been turned down.

 

[GoodDIYjob]

Yes, it looks like your FIL has been royally ripped off. Simple boiler swap would have done the trick!
From your sketch, the HW function of the combi is not being used (unless it's just not shown, the cold water in isn't shown either). Also if it's like that there will be a problem of unwanted flow through the rads when HW called. The CH return pipes should be commoned before the HW return connection.
If the house heating is poor, sounds like the 64° flow temperature is too low. Unlilkely, but worth checking the boiler output hasn't been turned down.

Thanks for the reply.

Yes, I think it would of been better, cheaper and more efficient. Given he is now heating hotwater in a tank he potentially doesn't use, depending on whether he uses the upstairs or downstairs bathroom, for showering or bathing. If he uses downstairs bathroom then the tanked hot water is wasted and he's paid twice for the hotwater.

I haven't shown cold water or Domestic hot water draw offs for simplicity of my scribbled down sketch. It could do with a bit more refinement to include all of that!

The combi dhw feeds downstairs bath, shower and basin and kitchen sink. It is hung in the kitchen.
The hot water cylinder feed upstairs shower and basin only. It is located in the airing cupboard where the pump (was) located previously as well.

I'm not sure my diagram shows the exact point of Actual commoning rad return on the system. I just sketched it as it seemed likely based on where I could see things visibly. But return connections were not very visible except the return of the indirect coil and bypass to flow. It is impossible to tell without lifting boards in the cylinder cupboard and probably removing some enclosure around the new boiler as it hides all the detail connections. In fact you can barely access the filling loop on the bottom of the boiler. The builder is coming back to create more access under the boiler by making a removable section of boxing in. Currently it is fixed and too restrictive.

My feeling was the 64C is not the key problem. As if the hotwater tank heating is not activated the rads are hot to touch top and bottom now (following balancing). However, running the hot water tank coil all the downstairs rads lose their heat. Seems more a question of flow.. But I agree, on subzero days he may need to increase flow to 70C as all the rads will be sized on the old flow temps expectations.

Thanks for the interest.

 

[fixitflav]

I haven't shown cold water or Domestic hot water draw offs for simplicity of my scribbled down sketch. It could do with a bit more refinement to include all of that!

OK thought so

I'm not sure my diagram shows the exact point of Actual commoning rad return on the system. I

If that part hasn't been changed and it was OK before, there shouldn't be a problem.

However, running the hot water tank coil all the downstairs rads lose their heat.

The HW circuit is likely to have much lower resistance than the rads, so if both valves are open most of the flow will go through the HW cylinder, which might explain it. I've always preferred W-plan with either/or 3-port valve and hot water preference, never found waiting for CH till the HW was satisfied to be a problem. Hot water preference could be arranged with your set-up, but a bit complicated, from your comments doubt if the guy involved would be up to it!

 

[GoodDIYjob]

OK thought so

If that part hasn't been changed and it was OK before, there shouldn't be a problem.

The HW circuit is likely to have much lower resistance than the rads, so if both valves are open most of the flow will go through the HW cylinder, which might explain it. I've always preferred W-plan with either/or 3-port valve and hot water preference, never found waiting for CH till the HW was satisfied to be a problem. Hot water preference could be arranged with your set-up, but a bit complicated, from your comments doubt if the guy involved would be up to it!

Yes. Could well be too much for the installer. I suppose what you are saying is a better way arranging pipework and of just ensuring the hw is activated separately to the heating.

He could program the morning or mid morning heating of hot water tank to be stand alone with out any rad call for heat. That is what I've got him doing at the moment with timer schedule settings.

Personally, on the system design, I think he should get someone back to feed the hot water tank and balanced cold to the bathroom. It is crazy to have the installed combi feeding the shower and bath downstairs. Total bonkers. I know this won't solve the hw coil priority issue we are discussing now though.

Thanks for the reply.

 

[Johntheo5]

There is really no reason why CH + HW won't work together, you will suffer some reduction of rad flow but not to the point of rads going cold as long as the pump head is sufficient, I have never gone around forensically measuring temperatures though. I have a A rated pump that displays the power in watts and can calculate the flowrate from this, A few years ago now but think I calculated ~ 15LPM with cyl + 7 rads on. 11LPM with cyl only on and 6 LPM with rads only, with pump running in a CP mode at 3.8M.