Radiators not heating up is it the pump or a blockage?

[webbm00]

In the current cold weather our heating system isn't heating up the radiators furthest away from the boiler. I'm not sure if it has always done this and we are only just noticing it or something has broken?

We have a Vaillant ecoTEC plus 637 system boiler. I've had a look at the d40 and d41 values. Boiler had been off for a little while but was warm, set to heating demand only:
D40 D41 Time
59 53 0
64 58 4 mins
75 64 5 mins - Fan and burner noise increases
79 70 15 mins
Then turn off and go into over run
Then it cycles through
D40 D41 Time
64 60 0
79 70 1-2 mins
Then turn off and go into over run

As the flow is reaching 80 I assume it is shuting down the boiler but why is it getting to 80? Is the boiler oversized and it's heating too quickly? Is the pump blocked?

What should I try to cure the problem before I have to call someone in?

 

[adlplumbing]

turn it on again and check tempture on the flow pipe with ur hand and see how quickly it moves heat if it very slow then pump has proably gone easy enough to change if you have the gear

 

[foxhole]

If the systems been idle the valves can seize, especially stat valves, open and close a few times and tap to see if they release. if it's an old system then sludge can block valves especially furthest from pump, is pump on full speed?

 

[webbm00]

turn it on again and check tempture on the flow pipe with ur hand and see how quickly it moves heat if it very slow then pump has proably gone easy enough to change if you have the gear

The flow pipe at the far radiator is hot. The return is cool?

If the systems been idle the valves can seize, especially stat valves, open and close a few times and tap to see if they release.

They are new Drayton TRV4 valves so I dont think they are stuck

if it's an old system then sludge can block valves especially furthest from pump, is pump on full speed?

It's an integrated 2 speed pump and I'm not sure how to change the speed of it.

 

[webbm00]

I found this post
//www.diynot.com/forums/viewtopic.php?t=139184&postdays=0&postorder=asc&start=15
That appears to be a similar problem. I'll try turning the power of the boiler down and see if that helps?

Also I'm not sure if it is relevant but my boiler is in the loft?

 

[JohnD]

if you have some hot radiators and some cool ones, start by turning the hot ones off or down and see if the cold ones heat up. Bear in mind that the lockshield valve needs adjusting when you are balancing radiators, not just the TRV or wheel-head

if you suspect your system to be dirty try a mild sediment-loosening cleaner such as Sentinel X400. It will cost you about £15. Run it for 4 weeks then drain and rinse. You will know the cleaner is starting to work if the circulating water goes jet black with loosened iron oxide. On final fill use a corrosion inhibitor such as X100.i

sediment is very common on old or open vented systems. If yours is new and sealed it is less likely to be dirty.

Also look for a by-pass which if too far open might be allowing too much water to short-circuit without going through the rads. I am not experienced in dealing with these, though, as I am not a pro. feel the flow and return pipes with your hand to see where the hot water is going to and from.

 

[webbm00]

if you have some hot radiators and some cool ones, start by turning the hot ones off or down and see if the cold ones heat up. Bear in mind that the lockshield valve needs adjusting when you are balancing radiators, not just the TRV or wheel-head

I've balanced them with the lockshield so they all heat up at the same time. It's just that they are not heating up that much or that quickly.

if you suspect your system to be dirty try a mild sediment-loosening cleaner such as Sentinel X400. It will cost you about £15. Run it for 4 weeks then drain and rinse. You will know the cleaner is starting to work if the circulating water goes jet black with loosened iron oxide. On final fill use a corrosion inhibitor such as X100.
sediment is very common on old or open vented systems. If yours is new and sealed it is less likely to be dirty.

I think this will be another next step as the system is a mix of old and new

Also look for a by-pass which if too far open might be allowing too much water to short-circuit without going through the rads. I am not experienced in dealing with these, though, as I am not a pro. feel the flow and return pipes with your hand to see where the hot water is going to and from.

It does have a bypass and it is set high enough that the water from it isn't hot

 

[webbm00]

Tried reducing the power of the boiler using d.0 down to 12KW. It made no difference. Still takes 15mins to get the flow up to 80 and switch off the boiler, then 2 minute cycle of boiler on heat flow up to 80 and into anti cycle mode.

The difference between flow and return is still 9-10deg.

Any ideas anyone?

 

[webbm00]

Also, I thought I would take the cap off of the front of the pump (internal to the boiler) and see if it was moving. I can't take the cap off as there is water under pressure behind it. I thought you should only have a little bit of water behind this cap?

 

[D_Hailsham]

Tried reducing the power of the boiler using d.0 down to 12KW.

Is 12kW just a "try it and see" number or have you worked out your heating requirement? If you haven't worked it out use the EST online boiler calculator

Still takes 15mins to get the flow up to 80 and switch off the boiler, then 2 minute cycle of boiler on heat flow up to 80 and into anti cycle mode.

Why are you trying to get a temperature of 80°C? If the difference is 10°C, the return will be 70°C, which is much too high for the boiler to condense.

Do you know the total kW of your radiators? Use Stelrad Elite Catalogue to find out.

Post the results of your boiler sizing and rad output calculations.

 

[webbm00]

Is 12kW just a "try it and see" number or have you worked out your heating requirement? If you haven't worked it out use the EST online boiler calculator

12KW is the lowest it goes to (37KW is max). I found a post on here with a rule of thumb of 1.4KW per rad giving 16.8KW for our house. I cant get the one on the link to work but tried the SEDBUK one which gave a value of 15.6KW so similar.

Why are you trying to get a temperature of 80°C? If the difference is 10°C, the return will be 70°C, which is much too high for the boiler to condense.

I'm not trying to get to 80 the boiler heats the flow up to 80 and then shuts down as it is it's max. I've not tried reducing the flow target temperature. Would this help? I'm not sure what you mean by "which is much too high for the boiler to condense"

Do you know the total kW of your radiators? Use Stelrad Elite Catalogue to find out.

About 19KW from a rough calculation

 

[D_Hailsham]

12KW is the lowest it goes to (37KW is max). I found a post on here with a rule of thumb of 1.4KW per rad giving 16.8KW for our house. I cant get the one on the link to work but tried the SEDBUK one which gave a value of 15.6KW so similar.

The Sedbuk and EST calculators are the same. Is 15.6kW the final result, i.e includes 2kW for hot water? If so then you need 13.6 kW for heating, say 14kW.

I'm not trying to get to 80 the boiler heats the flow up to 80 and then shuts down as it is it's max. I've not tried reducing the flow target temperature. Would this help? I'm not sure what you mean by "which is much too high for the boiler to condense"

Yes it would help to reduce the flow temperature.

A boiler will not condense if the return temperature is above approx 55C

About 19KW from a rough calculation

Is that from your 1.4kW rule of using the Stelrad data?

Assuming you have 19kW of rads and need 14kW for heating, you should have no problem achieving a temperature difference of 20 with a flow temp of 70C.

 

[webbm00]

The Sedbuk and EST calculators are the same. Is 15.6kW the final result, i.e includes 2kW for hot water? If so then you need 13.6 kW for heating, say 14kW.

Yes it includes 2KW for water.

A boiler will not condense if the return temperature is above approx 55C

So the return temp needs to stay below 55 for max efficiency and with the 10deg difference I'm seeing I'll try setting the max flow at 65 first.

Is that from your 1.4kW rule of using the Stelrad data?

Its from using data similar to the Stelrad file that I used when we built our extension

Assuming you have 19kW of rads and need 14kW for heating, you should have no problem achieving a temperature difference of 20 with a flow temp of 70C.

So why am I only seeing 10 deg difference? Any why do you think I should be getting 20 deg?

 

[webbm00]

So I set the target temp to 65 and now the boiler is on for 1 minute as the flow goes from 50 to 70 deg then it switches to pump over run for 3 mins and repeats.

My theory is that the pump is not man enough (or blocked/broken) to pump the water round the system quick enough to stop the flow from heating up and switching off the boiler. Would an external pump solve this as a problem?

 

[D_Hailsham]

So why am I only seeing 10 deg difference?

That's the puzzle.

You mention an extension.

Was the heating OK before you built it and added extra radiators?.

How much extra kW did you add?

Did you upgrade any of the existing pipes to allow for the extra load?

Have you balanced the system? How to Balance a CH System

why do you think I should be getting 20 deg?

The boiler's output is based on a temperature differential of 20°C.

You have 19kW of rads, but only need 14kW. 19kW of rads running at 70°/50°C will produce 14kW of heat.