How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • Go back-and-forth until satisfied
    Rate the answer you receive.
Ask Tim JA Your Own Question
Tim JA
Tim JA, Engineer
Category: Plumbing
Satisfied Customers: 3262
Experience:  Owner at Self-employed
Type Your Plumbing Question Here...
Tim JA is online now

Do the 2 heat exchangers in my combi boiler affect each

This answer was rated:

Do the 2 heat exchangers in my combi boiler affect each other? Ie if the main heat exchanger isnt cleaned properly on each service would the plate heat exchanger eventually get blocked?
Good morning, and welcome to Just Answer.The simple is answer is no.The secondary side of the DHW exchanger is independent from the main heat exchanger. The primary shares water with the main heat exchanger, and the rest of your heating system, but this water would not be cleaned during a boiler service.
Customer: replied 11 days ago.
Sorry jusy trying to get my head aroynd this! Which heat exchanger should be cleaned wirh each service as the service instructions do explain how to clean the heat exchanger?
To answer your question I need to look at the service instructions for your boiler.  What is the make and model?
Customer: replied 11 days ago.
Its a Viessmanm Vitodens 50 -W Type BPJC
Customer: replied 11 days ago.
Are you able to look at the service maintenance guidance for my boiler ok?
Customer: replied 11 days ago.
I have a couple of other questions about the boiler too?
1. What happens to the boiler if the installer fiited the magnetic filter to the feed pipework saying it didnt matter feed ir return. Anorher engineer changed pipework to the return? Can you explain what difference it makes please?
Customer: replied 11 days ago.
Lastly I live in a really hard water area Essex. Should he have fitted a swperate limescale filter too and would it make a difference? Thank you.

Sorry for the later reply - I was in all morning but out all afternoon.  I will read your posts and then reply.

Firstly, the heat exchanger cleaning that's referred to in the service instructions has nothing to do with the water pathways through either of the heat exchangers.  It's all about cleaning the combustion chamber and the surface of the main heat exchanger where the heat transfer starts.

To answer your other questions:

1 . What happens to the boiler if the installer fiited the magnetic filter to the feed pipework saying it didn't matter feed or return?
That depends on whether or not they followed the installation instructions for the magnetic filter.  I would expect those instructions to recommend fitting the filter on the return, but I don't know that for a fact.

2. Another engineer changed pipework to the return? Can you explain what difference it makes please?
The particles that the filter is designed to trap comes from the radiators, so the idea is stop those particles from reaching the boiler and baking onto the surface inside the heat exchanger.

3. Hard water area : Should he have fitted a separate limescale filter too?
If the boiler manufacturer recommends it for a hard water area, then yes.  Or, if in the opinion of the installer it is warranted, then yes.

4. Would it make a difference?
It depends on the product fitted, and the actual hardness rating of the water.

Customer: replied 11 days ago.
Also when the expansion vessel the boiler was replaced should the engineer have topped up the chemicals again as presumably he had to drain a fair amound of the system water out?

The usual method of replacing an expansion vessel inside the boiler casing is to isolate and drain the boiler.  Hardly any primary water is lost.

It feels to me that you don't really trust the person who you're paying to maintain your equipment.  If that's the case then you should not use them, but get someone you do trust.

Customer: replied 11 days ago.
you are right about that for sure. I have had no peace of mind with the problems on rhe boiler and seems like tge company fitting it were prettyuseless which has caused ongoing problems.
I will be getting a new boiler as soon as rjis one fails again with a reputable company this time! You have been really helpful to me. One other issue is that my rads have always been piping hot with no cold spots or problems but every few years theres no hot water and the plate heat exchanger has to be replaced to get the rads and hot water. They want me to have the system power flushed which costs £400/500 but why if my rads are fine and a plate heat exchanger is a £50 part easily changed?

It seems a bit cheeky to fail to maintain the system, but then recommend a costly power flush to remedy the result of their lack of care.  You need to find a heating engineer who will look after your best interests.

Customer: replied 11 days ago.
if you look at 5he service 8nayructions ti clean the heat exchanger it even says they should vacuum it not brush it. They have never done that either!
Why would the boiler plate heat exchanger block up when the rads are fine though?

"Why would it" is a question for whoever claims it's blocked.

Customer: replied 10 days ago.
The engineer says its because iI need the costly power flush. That's what i am trying to understand. Why only the boiler gets the problems of blocked plate heat exchanger?

5. "They want me to have the system power flushed which costs £400/500"
Flushing the system includes the radiators, so they are saying that the system is not fine.  The system includes the radiators.

6. "...a plate heat exchanger is a £50 part easily changed?"
The plate heat exchanger is for the hot water, and does not serve the radiators.  

7. "Why only the boiler gets the problems of blocked plate heat exchanger?"
If you're talking about the plate heat exchanger, it can scale up because it has fresh water passing through it, which has nothing to do with corrosion, or with the radiators, and cannot be removed by power flushing. A new one costs around £90, not £50. In many boilers it's not a lot more.

Again, all of your questions indicate that you don't believe the information being given to you by the engineer you're paying to maintain the system, who should be aiming to reduce your total cost of ownership.  If you don't trust them, then ignore what they're telling you and get someone better.

Customer: replied 10 days ago.
Will rate you 5 stars after this one as you have been so helpful. So just to clarify the plate heat exchanger icanr be blocked by water coming from the rads where is the stuff causing the blickage coming from?

IF the secondary side of the plate exchanger is blocked by scale, then it comes from the fresh water passing through it.  The harder the water, the faster it will scale up.  If your local water hardness is above 300ppm, then you need a polyphosphate-based dosing unit on the cold supply to the boiler.

Thank you for your rating :-)

Tim JA and 3 other Plumbing Specialists are ready to help you
Customer: replied 10 days ago.
Well i certainly understand a bit more about my boiler now! Thank you so much.

You're welcome. I'm pleased to hear you are another Happy Customer. If you would like to ask me another question in the future, you can add me as a favourite Expert.

Have a great weekend :-)