Central Heating Modifications – Set up . Commissioning

[GoodDIYjob]

Evening.

Father in law had an extension, this involved a extended single storey rear ext, approx. 4M x 4M heated by UFH.

A new boiler (Vaillant Ecotect Pure 825. No real idea why he accepted a combi, when he has a tank and solar which surpluses to hot water tank immersion, but moving on....

Adaptions - as pump was in airing cupboard in loft with hot water tank, new boiler has self contained pump, UFH manifold under boiler in kitchen cupboard, a bypass valve is fitted as shown in diagram between unzoned flow and Hot Water tank return in loft but set, I assume at default min 0.1bar. Loft header tank removed from boiler pipework as now pressurised.

Problems:

Keeping brief, the build went ok. Plumbing and central heating was fine until the older of the 2 man team was admitted to hospital ill and later died. Very unfortunate. Anyway, most of the build and 1st and a lot of second fix was done when that happened, but no commissioning / set up / wiring up.

Once the boiler was reconnected and put on, the remaining guy struggled to set it or even get it operating, with the existing nest thermostat and new heatmiser UFH thermostat.

He did get it working in end, but when cold weather hit in Decemeber, the heating in the house was "poor".

When I investigated I found:

• new towel rail in new bathroom lockshield closed – no heat
• Boiler set to 64C flow (hoping for condensing based on return temp I suppose)
• DHW temp set to 55C but could not get more than 40C out of thermostatic valve in new bathroom due to Cold Water flow being so high.
• Blend valve on underfloor heating set at 4.5, with a flow showing 52c and retrn 39C whilst still in later stages of heating. Seemed too high esp with Karndean floor coverings.
• No heat on downstairs radiators at all when UFH + Rads + Hot Water tank heating.
• Further investigation showed heating poorly balanced but even after balancing rads, downstairs rads not operative with hot water tank heating
• UFH pump Wilo Para 25/6 -43/SCU set to contant speed and curve 3.

Questions:

Trying to improve downstairs rad heat up and system operation.

I suggested thermos rad valves, at least upstairs, but FIL says why, when not needed before? Even regardless I still said they would improve control and efficiency.

Is the UFH single loop pump robbing flow set at 3 and on constant speed mode. Could that cause lack of flow for simultaneous HW tank coil heating? UFH on separate pump and single loop manifold - but flow has to come from main CH flow regardless?

The hw tank used to heat with rads and hot water cyclinder before on 12 year old baxi straight boiler, vented, separate pump (one of the first condensing ones).

I est. rads upstairs and downstairs combined do not exceed 10kwh.

UFH can’t be more than 1kwh (one loop) small room size - probably doesn't cover bathroom as towel rail installed.

Indirect hot water tank coil. No listed output on sticker on tank, only Litres and dimensions, but guess 8 or 9kwh. Takes about 1hr to heat to 60C and is 145L.

The installer is coming back Wednesday to try and improve but on the track record he will need some help to get it operating, at least as well as it used to.

I’m also left wondering, apart from possibly altering settings on the UFH wilo pump and lowering the curve setting, does the system now need a gate valve on the hot water tank return to slow down the tank flow and balance?

Thoughts? Thanks for any help. Most appreciated.

 

[Mister Banks]

The hot water tank isn't used with a combi boiler so why wasn't it, and the associated 2 port motorised valve, removed?

 

[fixitflav]

The hot water tank isn't used with a combi boiler so why wasn't it, and the associated 2 port motorised valve, removed?

As the OP says, doesn't know why he's got a combi (probably conned into it by an unscrupulous installer) but since he has, he could still use the CH output of the combi to heat the HW cylinder. Preferably arranged for HW preference, with different boiler control-stat settings for CH and HW. He could supply some of the hot taps from the combi direct, some from the HW cylinder, maybe useful to cater for high HW demand.

 

[Mister Banks]

As the OP says, doesn't know why he's got a combi (probably conned into it by an unscrupulous installer) but since he has, he could still use the CH output of the combi to heat the HW cylinder. Preferably arranged for HW preference, with different boiler control-stat settings for CH and HW. He could supply some of the hot taps from the combi direct, some from the HW cylinder, maybe useful to cater for high HW demand.

OK but wouldn't the installers have disconnected the HW cylinder from the hot feed to the taps? Needs some more info from OP.

 

[fixitflav]

Needs some more info from OP.

Agreed

 

[GoodDIYjob]

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.

 

[Johntheo5]

For a start suggest checking/setting the bypass to 0.25bar. Should look like something below.

 

[GoodDIYjob]

Yes. I will do it was set at 0.1. I didn't change it. But surprisingly, I couldn't feel much supply of heat going through it at any stage. Yes, it warmed up by conduction I suppose. But I could easily tououch it and the bridging pipework at all staged. Thanks for the advice.

 

[Johntheo5]

• UFH pump Wilo Para 25/6 -43/SCU set to contant speed and curve 3.

Suggest setting to curve 1 as you only have a one loop UFH, what flowrate is the flow meter (if fitted) showing?

Is the UFH single loop pump robbing flow set at 3 and on constant speed mode. Could that cause lack of flow for simultaneous HW tank coil heating? UFH on separate pump and single loop manifold - but flow has to come from main CH flow regardless?

Single loop should not rob as its flowrate is probably only 1 or 2 LPM (flow/return, boiler to manifold) but manifold pump should be wired to the UFH 2 port valve and not come on regardless.

 

[Johntheo5]

You (if) can access the boiler diagnostics and check the pump status, its default setting is 0( auto) , suggest changing to say 3 or 4.

 

[GoodDIYjob]

Suggest setting to curve 1 as you only have a one loop UFH, what flowrate is the flow meter (if fitted) showing?

Single loop should not rob as its flowrate is probably only 1 or 2 LPM (flow/return, boiler to manifold) but manifold pump should be wired to the UFH 2 port valve and not come on regardless.

Yes. Will move curve back to 1. Still on fixed speed? Not set differential pressure?

No flow meters!! It's the wilo pump, esbe mix valve backing plate and not much else. Very basic. Pic attached.

The ufh pump only comes on when ufh stat is calling for heat and the zone valve to it opens. As you'd expect.

 

[GoodDIYjob]

You (if) can access the boiler diagnostics and check the pump status, its default setting is 0( auto) , suggest changing to say 3 or 4.
View attachment 292292

Yes. I read those config settings. As not used to auto pump settings. It is on zero. If I change to 3 or 4 it said something about needing to change the setting in the bypass inside the boiler to max. Is that necessary as well? Thank you.

 

[Johntheo5]

Don't know if internal bypass needs adjusting, you can read off the pump speed in d.15, suggest checking this while pump still in auto at different combinations of CH, DHW&UFH, then change d.14 to say 3 and read off the speed, the pump head (a 7M pump?) is then 7 x (speed%)/100) squared, (the pump flow is directly proportional to the speed) and you will get a feel for what is required with the external by pass as well.

 

[GoodDIYjob]

Don't know if internal bypass needs adjusting, you can read off the pump speed in d.15, suggest checking this while pump still in auto at different combinations of CH, DHW&UFH, then change d.14 to say 3 and read off the speed, the pump head (a 7M pump?) is then 7 x (speed%)/100) squared, (the pump flow is directly proportional to the speed) and you will get a feel for what is required with the external by pass as well.

Will try that. Thanks. Or maybe suggest to engineer on his revisit. Either way gives me something to work with.

You think a gate valve on the hot water tank coil should not be necessary? There wasn't one there in the past set up. ?

Thanks a lot..

 

[Johntheo5]

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?.