BG or local rgi for install?

[bengasman]

...BG will fit a Vaillant837 and give two years homecare free. ...

That is fantastically generous of them. Especially compared with the 5 years warrantee you get if you use a good independent. In other words, you pay £600 more for 3 years less warrantee.

 

[bengasman]

...Now if I am reading this right this means that it has to be below -1C for it to be working efficiently?...

No, whether or not the boiler works at or near maximum efficiency depends on the setting of the boiler, and the tuning of the rads. It has little or nothing to do with the outside temperature.

 

[bluey831]

hi bluey

Just reading your posts for a change.

Hey now fluff .. fancy meeting you on my thread!!!

I must insist on your best behaviour in here girl .... no messing around on this thread - we get the business done.

 

[bluey831]

Put another way what is the difference between the heat loss of the house (13.5kw) and the heat that the rads give out (15.3kw).

Heat loss of the house is calculated as the amount of heat needed to raise the temperature from -1C to 20C and maintain 20C. If the outside temperature is lower, more heat is required; if higher then less. The heat required is approximately proportional to the difference between outside and room temperatures.

So if the heat loss is 13.5kW, that means that your radiators need to produce 13.5kW to heat the house from -1C to 20C and keep it at 20C. If the rads give out 15.3kW it will do two things: heat the house from a lower temperature (approx -4C) to 20C, or heat the house up faster if the outside temperature is higher.

Ya know what ..... I think I have got it. Excellent explanation.

 

[bluey831]

...BG will fit a Vaillant837 and give two years homecare free. ...

That is fantastically generous of them. Especially compared with the 5 years warrantee you get if you use a good independent. In other words, you pay £600 more for 3 years less warrantee.

Ben - this has been my dilemma. You see I get Homecare on a good deal at £11 per month or £132 per year - all parts, labour and service. Now a service is in the region of £60 which I would have to pay anyway. This means I am paying an additional £72 per year for the final three years and that gives me full warranty on the Boiler and CH.

There are two main issues swaying me towards BG and away from an RGI. One - the house is old, they system is old and I dont know what unforseens is going to turn up on the job. To some extent an RGI is limited to how much time and resources he can spend on the job before it becomes a loser. The other thing of course is the dependability of getting the RGI back to resolve any issues afterwards - though that is a lesser of a concern.

I have got it down to BG being down to about £500 - £600 more expensive. The question is what value the risk of above issues.

 

[bluey831]

Well.... I done the deed and got me a Vailant 837 and done the flush. So far more than happy with the Central Heating side of it - all rads coming warming up nicely.

Disappointed with the shower though. The pressure is less than we had with a 2 Bar pump before the Combi. It is just about sufficient to have a shower but not what we are used to. The engineer did say that the shower was just a 'bar shower' and as such was mixing the water at the shower and thus not letting as much water through. I am assuming this was what it was doing when the pump was on also but it was forcing it through. He mentioned about getting a Mira shower which would allow more water through and thus better pressure.

With the shower head off I am getting about 14 -15 litres per minute through when the thermostat is set to 0 degrees. If I set it to about 38 degrees, it is coming through at about 11-12 litres per minute.

Any suggestions on what I need to do to get a better pressure through on the shower?

Thanks in advance.

 

[Tibbot]

You're confusing pressure with flow rate. Did the nice BG people not explain the difference to you?

 

[bluey831]

Tibbot - I might be indeed. However, I have had a few around and have asked on this forum etc and by all accounts I was under the impression the important thing was the flow rate into the house. This is about 20 litres per minute.

Now are you saying I can have better pressure with the same flow rate on a different shower? If there is 10 -15 litres per minute getting to the shower does the shower itself and the shower head create the pressure and thus give a more forceful shower?

Or am I totally on the wrong track .....

 

[Tibbot]

You can increase the flow rate if you could increase the pressure but you can't increase the pressure by increasing the flow rate. It remains the same.

By strangling the spray you simply increase the force that's applied out the hole but it's always less than the standing pressure available.

PS. Have you checked the incoming mains pressure?

 

[bluey831]

Yes - have checked mains pressure and it is about 20 litres per minute. I'm told that is reasonably good pressure. Thats why I'm figuring I should be able to get the equivalent of the pumped shower I previously had.

Trouble is I don't know what it is I need to change to do that i.e. shower, shower head or something else.

 

[Tibbot]

Yes - have checked mains pressure and it is about 20 litres per minute. I'm told that is reasonably good pressure.

That's not pressure it's the flow rate. Has anyone mentioned or measured your pressure, expressed in bar or psi?

In any case your shower pump was capable of pushing HW @ 2 bar out of a 22mm tap at 65 degree stored temp. Your combi won't match that.

 

[bluey831]

Nope - pretty much everyone measured the flow rate i.e. jug under tap.

How do I measure the pressure then? It sounds like from what you are saying I aint gonna get it any better than it is? Was hoping to have it near the equivalent of the pumped version but currently it would seem to be about half that.

 

[Tibbot]

You measure pressure with a pressure gauge. If you've 20l/min flow chances are you'll have adequate pressure behind to supply combi so it performs to manufacturers design. Some combis are max flow restricted to supply only what it can heat eg. 15l/min at 35 degree rise from incoming temp. Well short of pre-heated pumped stored HW.

 

[bluey831]

I dont know if the Vailaint 837 is max flow restricted or what effect that has? I think its capacity is about 13l per min.

Where would I get a pressure guage?

The question is would changing shower from a Bristan bar shower to a Mira with a bigger flow throughput make any difference?

 

[Tibbot]

Where would I get a pressure guage?
The question is would changing shower from a Bristan bar shower to a Mira with a bigger flow throughput make any difference?

Gauge locally to you I don't know

Can't be sure of shower because we don't know your mains pressure.