Replacement radiator is colder at bottom than it is at top.

[D_Hailsham]

All TRV's are set to maximum. The house never get warm enough to have them lower.

That's put paid to a theory I had that possibly the TRVs on the other rads were closing before the TRV on the dining rad. The effect of this would be to increase the pressure in the system so the flow rate would slow down. A lower flow rate will give a higher temperature differential, which is what you have.

I have never seen the boiler switch to a small flame either on hot water or heating. Does this lead back to DH's original theory on the boiler not being able to modulate low enough?

The size of the flame may not be a reliable indicator; the gas rate is.

Let the boiler cool right down and the start it up with the temperature dial set to 9. Make a note of the gas meter reading every 30 seconds until the boiler cuts out. Then work out, by subtraction, how much is used every 30 seconds. If the boiler is modulating correctly, you should find the consumption will stay constant for a period and then start reducing.

 

[tamz]

Repipe the problem rads in 15mm. Fit a drain valve to outside while you/they are at it. Rebalance the system properly.
Get on to Alpha (who i believe you said you had a service contract with) and tell them the boiler is not modulating.
In the meantime stop playing with it and leave the system as it is.

Never had tablet for years. My mother used to make it for the guysers

 

[fluff29]

DH - will try the gas tonight.

Tamz - I am thinking the same as you. Would you recommend 10 or 15 mm for this size of rad or is it bigger the better with regards to piping?

I have only learnt how to make table and the recipe is perfect. Going to cost me a fortune in dental bills.

 

[ChrisR]

would a wrongly adjusted gas valve stop the boiler from modulating and keep the boiler on full all the time.

Full until it cut out because it's too hot.

 

[tamz]

DH - will try the gas tonight.

Tamz - I am thinking the same as you. Would you recommend 10 or 15 mm for this size of rad or is it bigger the better with regards to piping?
/quote]

10mm will generally do around 4kw (depending on length) but 15mm plastic is just as cheap and easy to install and will give guaranteed flow.

If you had offered to let me scrape the hot tablet pot i might have come up

 

[fluff29]

Tamz, would make numerous amounts of tablet for takeaway, if I just get this fixed.

Will be contracting locals today for repipe, fit drain tap & cleanse the system.

My boiler does modulate. Ran it on full for 18.28 mins, 3 mins off then 4.12mins.

I checked the gas meter every 30 secs as DH said. The boiler ran as follows:-

1st run
1 min at 0.016 per 30 secs (first minute of start up)
3 mins at 0.022 per 30 secs
3.5 mins at 0.020 per 30 secs
2 mins at 0.018 per 30 secs
1.5 mins @ 0.016 per 30 secs
1 min at 0.015 per 30 secs
6 mins @ 0.014/0.013 per 30 secs

2nd run
Boiler ran at around 0.014/0.013 for the whole time

Everywhere heated well, the big rad did have abit more heat in the bottom than it does at 7 but I can't ran the boiler at 9 all the time. I would become bankrupt.

fluff

 

[DP]

*Boiler - Flow F87.8 Return R43.7
*Kitchen - F79.3 R49.7
*Dining Rm - F81.9 R41.9
*Living Rm - F84.0 R50.3
*Bathroom - 80.3 R74.5
*Hall - F82.2 R49.1
*Daughters room - F80.7 R56.0
*My room - F79.7 R51.3

From above 'my room' temperature differential is 28 degrees. Rest of the radiators are not much better apart from bathroom which has a differential of only 6 degrees.

Based on what has been posted on this thread to date, cannot see how replumbing one radiator is going to make things better. Temperature differential across flow and return is 43 degrees

 

[fluff29]

DP - you are thinking the same as me, but husband agrees with Tamz.

I just do not see how repiping this rad will improve the flow throughout the system and also how will it prevent the boiler switching off before the rads heat up when on number 4 or 5.

If I turn the problem rad off and put the heating to no.4, the heating will still switch off after a very short time. That can't be right as surely the boiler should stay on until all the rads are hot?

DP, after my hubby and Tamz convinces me, you come along and convince me otherwise.

 

[D_Hailsham]

I checked the gas meter every 30 secs. The boiler ran as follows:-

1st run
20.54kW 1 min at 0.016 per 30 secs (first minute of start up)
28.25kW 3 mins at 0.022 per 30 secs
25.7kW 3.5 mins at 0.020 per 30 secs
23.11kW 2 mins at 0.018 per 30 secs
20.54 1.5 mins @ 0.016 per 30 secs
19.26kW 1 min at 0.015 per 30 secs
17.98/16.7kW 6 mins @ 0.014/0.013 per 30 secs

2nd run
17.98/16.7kW Boiler ran at around 0.014/0.013 for the whole time

I have shown the power in to the boiler; power out is about 80%. So the lowest it went to was about 13.3kW

The boiler may be modulating down. But why is it stopping at 13.3kW and not going all the way down to 11kW?

 

[tamz]

*Boiler - Flow F87.8 Return R43.7
*Kitchen - F79.3 R49.7
*Dining Rm - F81.9 R41.9
*Living Rm - F84.0 R50.3
*Bathroom - 80.3 R74.5
*Hall - F82.2 R49.1
*Daughters room - F80.7 R56.0
*My room - F79.7 R51.3

Based on what has been posted on this thread to date, cannot see how replumbing one radiator is going to make things better. Temperature differential across flow and return is 43 degrees

Danny the above figures were from after the system had been "balanced".

The temperature differentials were far too great and presuming the pipes are unlagged and with the amount of throttling back they would drop more heat on the way back so the 44 deg at the boiler would be a reasonable expectation.

The system has now been opened up again allowing the water to flow more freely. The dining room rad pipes are undersized and the 2 big bedroom rads are borderline.
Repiping the dinning room rad ( the 2 bedroom ones could do with it too) will allow more flow and it will fully heat.
The system can then be balanced properly.

Fluff.
The boiler will not ignite and stay on continually until the full house is up to temperature. That is not how it works. The output would have to modulate really low for that to happen.
As the rads and room heat up the outputs drop so the temperature of the water rises to a point where the boiler is producing more than can be dumped around the system and has to cut out for a bit. This is quite normal.

 

[Agile]

The boiler should modulate to a gas rate of about 33% of the maximum.

Your boiler is not modulating enough. That would usually be as a result of a wrongly set gas valve. Thast needs a competent engineer to adust it. Many dont know how to do it.

But thats only part of your problem. The temperature, and thus by deduction, the flow rate through your rads is far too low so there is a significant circulation problem.

Unfortunately with an 8mm system its not always easy to guess what a correct system can achieve. It all depends on the layout and pipe lengths. All I can say is that many work passably well but circulation problems are common.

I recently fitted a new boiler on a small four rad and two towel rail system and it works fine.

Tony

 

[joop1977]

Blockage in system or boiler,get someone to sort it,this thread has gone on far too long ffs

 

[Agile]

She did say that some dirt came out when she did the bucket test.

I dont remember seeing it stated anywhere that the impeller of the pump has been opened and inspected for debris.

Tony

 

[DP]

Tony, you are writing without thinking. If the pump was blocked or whatever, HW demand would not clock the gas rate that has been documented. Anyway, pump, I believe has been replaced

Fluff, can you do something so this thread can come to an end. It is becoming a sopa saga.

 

[Agile]

I did think Danny.

Generally if the pump is sluggish or part blocked on DHW it still works reasonably well but the temperature differential between the primary and secondary increases.

I know its not quite the same arrangement but remember how a Puma does DHW with no pump working.

If the pump has been changed then that probably eliminates that.

Of course with 8mm microbore the full pumping ability is all the more critical.

Tony